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 $232.78   11.779%   $260.1992   $260.20   $260.20   $260.20  
  Purchase #2 $146.51   3.793%   $152.0671   $152.07   $152.05   $152.10  
  Purchase #3 $101.34   12.239%   $113.743   $113.74   $113.75   $113.70  
  Purchase #4 $26.72   10.168%   $29.4369   $29.44   $29.45   $29.40  
  Purchase #5 $98.78   4.228%   $102.9564   $102.96   $102.95   $103.00  
  Purchase #6 $203.87   13.437%   $231.264   $231.26   $231.25   $231.30  
  Purchase #7 $124.42   7.194%   $133.3708   $133.37   $133.35   $133.40  
  7 purchase totals = $934.42       $1,023.0374   $1,023.04   $1,023.00   $1,023.10