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 $56.73   11.577%   $63.2976   $63.30   $63.30   $63.30  
  Purchase #2 $225.75   8.484%   $244.9026   $244.90   $244.90   $244.90  
  Purchase #3 $195.73   3.633%   $202.8409   $202.84   $202.85   $202.80  
  Purchase #4 $64.53   12.299%   $72.4665   $72.47   $72.45   $72.50  
  Purchase #5 $180.89   9.426%   $197.9407   $197.94   $197.95   $197.90  
  Purchase #6 $203.30   10.601%   $224.8518   $224.85   $224.85   $224.90  
  Purchase #7 $9.43   7.494%   $10.1367   $10.14   $10.15   $10.10  
  7 purchase totals = $936.36       $1,016.4368   $1,016.44   $1,016.45   $1,016.40