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 $224.86   9.693%   $246.6557   $246.66   $246.65   $246.70  
  Purchase #2 $209.33   8.303%   $226.7107   $226.71   $226.70   $226.70  
  Purchase #3 $23.71   12.369%   $26.6427   $26.64   $26.65   $26.60  
  Purchase #4 $64.38   6.247%   $68.4018   $68.40   $68.40   $68.40  
  Purchase #5 $100.31   3.487%   $103.8078   $103.81   $103.80   $103.80  
  Purchase #6 $47.55   13.850%   $54.1357   $54.14   $54.15   $54.10  
  Purchase #7 $210.71   12.783%   $237.6451   $237.65   $237.65   $237.60  
  7 purchase totals = $880.85       $963.9995   $964.01   $964.00   $963.90