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 $62.39   11.124%   $69.3303   $69.33   $69.35   $69.30  
  Purchase #2 $166.78   7.507%   $179.3002   $179.30   $179.30   $179.30  
  Purchase #3 $141.71   13.731%   $161.1682   $161.17   $161.15   $161.20  
  Purchase #4 $153.64   8.505%   $166.7071   $166.71   $166.70   $166.70  
  Purchase #5 $231.75   7.726%   $249.655   $249.66   $249.65   $249.70  
  Purchase #6 $201.58   13.814%   $229.4263   $229.43   $229.45   $229.40  
  Purchase #7 $90.94   10.382%   $100.3814   $100.38   $100.40   $100.40  
  7 purchase totals = $1,048.79       $1,155.9685   $1,155.98   $1,156.00   $1,156.00