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 $55.37   8.650%   $60.1595   $60.16   $60.15   $60.20  
  Purchase #2 $31.92   7.595%   $34.3443   $34.34   $34.35   $34.30  
  Purchase #3 $229.66   5.748%   $242.8609   $242.86   $242.85   $242.90  
  Purchase #4 $55.59   13.421%   $63.0507   $63.05   $63.05   $63.10  
  Purchase #5 $236.49   13.737%   $268.9766   $268.98   $269.00   $269.00  
  Purchase #6 $146.86   13.474%   $166.6479   $166.65   $166.65   $166.60  
  Purchase #7 $121.53   8.738%   $132.1493   $132.15   $132.15   $132.10  
  7 purchase totals = $877.42       $968.1892   $968.19   $968.20   $968.20