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 $69.82   7.253%   $74.884   $74.88   $74.90   $74.90  
  Purchase #2 $236.55   7.822%   $255.0529   $255.05   $255.05   $255.10  
  Purchase #3 $94.96   7.703%   $102.2748   $102.27   $102.25   $102.30  
  Purchase #4 $223.60   6.331%   $237.7561   $237.76   $237.75   $237.80  
  Purchase #5 $141.74   11.262%   $157.7028   $157.70   $157.70   $157.70  
  Purchase #6 $37.83   8.154%   $40.9147   $40.91   $40.90   $40.90  
  Purchase #7 $68.98   13.441%   $78.2516   $78.25   $78.25   $78.30  
  7 purchase totals = $873.48       $946.8369   $946.82   $946.80   $947.00