Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $114.69   10.112%   $126.2875   $126.29   $126.30   $126.30  
  Purchase #2 $201.47   13.616%   $228.9022   $228.90   $228.90   $228.90  
  Purchase #3 $232.41   11.527%   $259.1999   $259.20   $259.20   $259.20  
  Purchase #4 $162.78   10.299%   $179.5447   $179.54   $179.55   $179.50  
  Purchase #5 $147.42   5.368%   $155.3335   $155.33   $155.35   $155.30  
  Purchase #6 $232.38   13.406%   $263.5329   $263.53   $263.55   $263.50  
  Purchase #7 $129.46   3.261%   $133.6817   $133.68   $133.70   $133.70  
  7 purchase totals = $1,220.61       $1,346.4824   $1,346.47   $1,346.55   $1,346.40