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 $61.94   3.424%   $64.0608   $64.06   $64.05   $64.10  
  Purchase #2 $141.31   11.840%   $158.0411   $158.04   $158.05   $158.00  
  Purchase #3 $104.86   12.475%   $117.9413   $117.94   $117.95   $117.90  
  Purchase #4 $230.99   8.771%   $251.2501   $251.25   $251.25   $251.30  
  Purchase #5 $27.28   6.277%   $28.9924   $28.99   $29.00   $29.00  
  Purchase #6 $236.31   7.243%   $253.4259   $253.43   $253.45   $253.40  
  Purchase #7 $136.76   7.137%   $146.5206   $146.52   $146.50   $146.50  
  7 purchase totals = $939.45       $1,020.2322   $1,020.23   $1,020.25   $1,020.20