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 $224.27   8.681%   $243.7389   $243.74   $243.75   $243.70  
  Purchase #2 $131.76   13.519%   $149.5726   $149.57   $149.55   $149.60  
  Purchase #3 $136.49   3.732%   $141.5838   $141.58   $141.60   $141.60  
  Purchase #4 $169.67   12.409%   $190.7244   $190.72   $190.70   $190.70  
  Purchase #5 $140.35   10.411%   $154.9618   $154.96   $154.95   $155.00  
  Purchase #6 $40.95   11.720%   $45.7493   $45.75   $45.75   $45.70  
  Purchase #7 $106.46   10.727%   $117.88   $117.88   $117.90   $117.90  
  7 purchase totals = $949.95       $1,044.2108   $1,044.20   $1,044.20   $1,044.20