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 $87.92   6.404%   $93.5504   $93.55   $93.55   $93.60  
  Purchase #2 $234.38   8.353%   $253.9578   $253.96   $253.95   $254.00  
  Purchase #3 $18.77   10.161%   $20.6772   $20.68   $20.70   $20.70  
  Purchase #4 $39.60   8.678%   $43.0365   $43.04   $43.05   $43.00  
  Purchase #5 $48.87   10.414%   $53.9593   $53.96   $53.95   $54.00  
  Purchase #6 $211.95   8.166%   $229.2578   $229.26   $229.25   $229.30  
  Purchase #7 $138.97   11.836%   $155.4185   $155.42   $155.40   $155.40  
  7 purchase totals = $780.46       $849.8575   $849.87   $849.85   $850.00