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 $192.65   6.115%   $204.4305   $204.43   $204.45   $204.40  
  Purchase #2 $155.96   6.135%   $165.5281   $165.53   $165.55   $165.50  
  Purchase #3 $47.84   3.229%   $49.3848   $49.38   $49.40   $49.40  
  Purchase #4 $144.50   10.874%   $160.2129   $160.21   $160.20   $160.20  
  Purchase #5 $71.93   13.191%   $81.4183   $81.42   $81.40   $81.40  
  Purchase #6 $54.94   4.596%   $57.465   $57.47   $57.45   $57.50  
  Purchase #7 $33.90   3.316%   $35.0241   $35.02   $35.00   $35.00  
  7 purchase totals = $701.72       $753.4637   $753.46   $753.45   $753.40