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 $228.68   8.162%   $247.3449   $247.34   $247.35   $247.30  
  Purchase #2 $137.26   11.571%   $153.1424   $153.14   $153.15   $153.10  
  Purchase #3 $155.74   5.485%   $164.2823   $164.28   $164.30   $164.30  
  Purchase #4 $207.95   11.653%   $232.1824   $232.18   $232.20   $232.20  
  Purchase #5 $59.46   11.122%   $66.0731   $66.07   $66.05   $66.10  
  Purchase #6 $94.61   7.601%   $101.8013   $101.80   $101.80   $101.80  
  Purchase #7 $52.53   9.478%   $57.5088   $57.51   $57.50   $57.50  
  7 purchase totals = $936.23       $1,022.3352   $1,022.32   $1,022.35   $1,022.30