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 $60.56   13.648%   $68.8252   $68.83   $68.85   $68.80  
  Purchase #2 $237.31   4.201%   $247.2794   $247.28   $247.30   $247.30  
  Purchase #3 $22.77   3.578%   $23.5847   $23.58   $23.60   $23.60  
  Purchase #4 $95.40   6.560%   $101.6582   $101.66   $101.65   $101.70  
  Purchase #5 $19.93   10.188%   $21.9605   $21.96   $21.95   $22.00  
  Purchase #6 $68.72   7.604%   $73.9455   $73.95   $73.95   $73.90  
  Purchase #7 $239.89   9.228%   $262.027   $262.03   $262.05   $262.00  
  7 purchase totals = $744.58       $799.2805   $799.29   $799.35   $799.30