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 $242.32   9.505%   $265.3525   $265.35   $265.35   $265.40  
  Purchase #2 $221.87   13.389%   $251.5762   $251.58   $251.60   $251.60  
  Purchase #3 $62.53   4.480%   $65.3313   $65.33   $65.35   $65.30  
  Purchase #4 $230.82   11.124%   $256.4964   $256.50   $256.50   $256.50  
  Purchase #5 $125.75   7.598%   $135.3045   $135.30   $135.30   $135.30  
  Purchase #6 $141.90   7.195%   $152.1097   $152.11   $152.10   $152.10  
  Purchase #7 $230.99   3.343%   $238.712   $238.71   $238.70   $238.70  
  7 purchase totals = $1,256.18       $1,364.8826   $1,364.88   $1,364.90   $1,364.90