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 $208.64   12.694%   $235.1248   $235.12   $235.10   $235.10  
  Purchase #2 $42.61   13.688%   $48.4425   $48.44   $48.45   $48.40  
  Purchase #3 $155.54   4.588%   $162.6762   $162.68   $162.70   $162.70  
  Purchase #4 $210.48   11.830%   $235.3798   $235.38   $235.40   $235.40  
  Purchase #5 $176.92   13.634%   $201.0413   $201.04   $201.05   $201.00  
  Purchase #6 $5.48   10.359%   $6.0477   $6.05   $6.05   $6.00  
  Purchase #7 $114.60   7.449%   $123.1366   $123.14   $123.15   $123.10  
  7 purchase totals = $914.27       $1,011.8489   $1,011.85   $1,011.90   $1,011.70