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 $57.95   7.782%   $62.4597   $62.46   $62.45   $62.50  
  Purchase #2 $218.39   11.791%   $244.1404   $244.14   $244.15   $244.10  
  Purchase #3 $138.61   11.640%   $154.7442   $154.74   $154.75   $154.70  
  Purchase #4 $110.77   13.484%   $125.7062   $125.71   $125.70   $125.70  
  Purchase #5 $137.43   10.531%   $151.9028   $151.90   $151.90   $151.90  
  Purchase #6 $221.58   3.739%   $229.8649   $229.86   $229.85   $229.90  
  Purchase #7 $196.31   4.746%   $205.6269   $205.63   $205.65   $205.60  
  7 purchase totals = $1,081.04       $1,174.4451   $1,174.44   $1,174.45   $1,174.40