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 $69.83   6.433%   $74.3222   $74.32   $74.30   $74.30  
  Purchase #2 $207.89   10.148%   $228.9867   $228.99   $229.00   $229.00  
  Purchase #3 $244.32   10.712%   $270.4916   $270.49   $270.50   $270.50  
  Purchase #4 $78.78   6.699%   $84.0575   $84.06   $84.05   $84.10  
  Purchase #5 $63.35   4.213%   $66.0189   $66.02   $66.00   $66.00  
  Purchase #6 $125.65   12.406%   $141.2381   $141.24   $141.25   $141.20  
  Purchase #7 $135.89   9.797%   $149.2031   $149.20   $149.20   $149.20  
  7 purchase totals = $925.71       $1,014.3181   $1,014.32   $1,014.30   $1,014.30