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 $145.80   7.230%   $156.3413   $156.34   $156.35   $156.30  
  Purchase #2 $230.37   11.810%   $257.5767   $257.58   $257.60   $257.60  
  Purchase #3 $227.82   9.389%   $249.21   $249.21   $249.20   $249.20  
  Purchase #4 $76.53   12.202%   $85.8682   $85.87   $85.85   $85.90  
  Purchase #5 $208.56   6.443%   $221.9975   $222.00   $222.00   $222.00  
  Purchase #6 $212.27   11.198%   $236.04   $236.04   $236.05   $236.00  
  Purchase #7 $46.33   4.730%   $48.5214   $48.52   $48.50   $48.50  
  7 purchase totals = $1,147.68       $1,255.5551   $1,255.56   $1,255.55   $1,255.50