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 $12.84   10.754%   $14.2208   $14.22   $14.20   $14.20  
  Purchase #2 $214.47   8.322%   $232.3182   $232.32   $232.30   $232.30  
  Purchase #3 $111.66   4.571%   $116.764   $116.76   $116.75   $116.80  
  Purchase #4 $62.95   13.687%   $71.566   $71.57   $71.55   $71.60  
  Purchase #5 $126.40   9.360%   $138.231   $138.23   $138.25   $138.20  
  Purchase #6 $21.80   4.190%   $22.7134   $22.71   $22.70   $22.70  
  Purchase #7 $207.46   9.507%   $227.1832   $227.18   $227.20   $227.20  
  7 purchase totals = $757.58       $822.9966   $822.99   $822.95   $823.00