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 $174.69   11.208%   $194.2693   $194.27   $194.25   $194.30  
  Purchase #2 $180.35   10.299%   $198.9242   $198.92   $198.90   $198.90  
  Purchase #3 $141.94   5.163%   $149.2684   $149.27   $149.25   $149.30  
  Purchase #4 $47.97   7.119%   $51.385   $51.39   $51.40   $51.40  
  Purchase #5 $245.93   11.227%   $273.5406   $273.54   $273.55   $273.50  
  Purchase #6 $58.81   13.147%   $66.5418   $66.54   $66.55   $66.50  
  Purchase #7 $91.78   3.592%   $95.0767   $95.08   $95.10   $95.10  
  7 purchase totals = $941.47       $1,029.0060   $1,029.01   $1,029.00   $1,029.00