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 $120.52   5.137%   $126.7111   $126.71   $126.70   $126.70  
  Purchase #2 $121.71   6.693%   $129.8561   $129.86   $129.85   $129.90  
  Purchase #3 $51.78   6.214%   $54.9976   $55.00   $55.00   $55.00  
  Purchase #4 $79.87   5.389%   $84.1742   $84.17   $84.15   $84.20  
  Purchase #5 $169.54   9.591%   $185.8006   $185.80   $185.80   $185.80  
  Purchase #6 $178.98   5.532%   $188.8812   $188.88   $188.90   $188.90  
  Purchase #7 $149.88   9.809%   $164.5817   $164.58   $164.60   $164.60  
  7 purchase totals = $872.28       $935.0025   $935.00   $935.00   $935.10