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 $53.91   10.494%   $59.5673   $59.57   $59.55   $59.60  
  Purchase #2 $211.98   11.704%   $236.7901   $236.79   $236.80   $236.80  
  Purchase #3 $151.29   4.687%   $158.381   $158.38   $158.40   $158.40  
  Purchase #4 $200.39   12.389%   $225.2163   $225.22   $225.20   $225.20  
  Purchase #5 $216.75   9.653%   $237.6729   $237.67   $237.65   $237.70  
  Purchase #6 $92.41   8.221%   $100.007   $100.01   $100.00   $100.00  
  Purchase #7 $203.44   8.488%   $220.708   $220.71   $220.70   $220.70  
  7 purchase totals = $1,130.17       $1,238.3426   $1,238.35   $1,238.30   $1,238.40