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 $62.86   11.424%   $70.0411   $70.04   $70.05   $70.00  
  Purchase #2 $116.37   10.683%   $128.8018   $128.80   $128.80   $128.80  
  Purchase #3 $33.79   10.682%   $37.3994   $37.40   $37.40   $37.40  
  Purchase #4 $134.39   13.433%   $152.4426   $152.44   $152.45   $152.40  
  Purchase #5 $151.88   4.273%   $158.3698   $158.37   $158.35   $158.40  
  Purchase #6 $240.99   8.345%   $261.1006   $261.10   $261.10   $261.10  
  Purchase #7 $22.82   10.119%   $25.1292   $25.13   $25.15   $25.10  
  7 purchase totals = $763.10       $833.2845   $833.28   $833.30   $833.20