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 $208.93   12.265%   $234.5553   $234.56   $234.55   $234.60  
  Purchase #2 $144.48   3.323%   $149.2811   $149.28   $149.30   $149.30  
  Purchase #3 $71.42   11.609%   $79.7111   $79.71   $79.70   $79.70  
  Purchase #4 $124.54   8.571%   $135.2143   $135.21   $135.20   $135.20  
  Purchase #5 $211.91   8.622%   $230.1809   $230.18   $230.20   $230.20  
  Purchase #6 $102.47   4.448%   $107.0279   $107.03   $107.05   $107.00  
  Purchase #7 $91.68   11.588%   $102.3039   $102.30   $102.30   $102.30  
  7 purchase totals = $955.43       $1,038.2745   $1,038.27   $1,038.30   $1,038.30