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 $181.99   8.624%   $197.6848   $197.68   $197.70   $197.70  
  Purchase #2 $56.93   9.286%   $62.2165   $62.22   $62.20   $62.20  
  Purchase #3 $215.90   11.404%   $240.5212   $240.52   $240.50   $240.50  
  Purchase #4 $146.54   9.811%   $160.917   $160.92   $160.90   $160.90  
  Purchase #5 $95.70   3.229%   $98.7902   $98.79   $98.80   $98.80  
  Purchase #6 $105.28   4.746%   $110.2766   $110.28   $110.30   $110.30  
  Purchase #7 $141.39   5.650%   $149.3785   $149.38   $149.40   $149.40  
  7 purchase totals = $943.73       $1,019.7848   $1,019.79   $1,019.80   $1,019.80