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 $51.82   11.672%   $57.8684   $57.87   $57.85   $57.90  
  Purchase #2 $227.81   12.494%   $256.2726   $256.27   $256.25   $256.30  
  Purchase #3 $113.42   12.169%   $127.2221   $127.22   $127.20   $127.20  
  Purchase #4 $93.60   5.436%   $98.6881   $98.69   $98.70   $98.70  
  Purchase #5 $145.86   4.538%   $152.4791   $152.48   $152.50   $152.50  
  Purchase #6 $102.80   12.272%   $115.4156   $115.42   $115.40   $115.40  
  Purchase #7 $103.43   13.368%   $117.2565   $117.26   $117.25   $117.30  
  7 purchase totals = $838.74       $925.2024   $925.21   $925.15   $925.30