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 $111.34   13.755%   $126.6548   $126.65   $126.65   $126.70  
  Purchase #2 $210.55   6.403%   $224.0315   $224.03   $224.05   $224.00  
  Purchase #3 $44.54   5.502%   $46.9906   $46.99   $47.00   $47.00  
  Purchase #4 $245.39   4.683%   $256.8816   $256.88   $256.90   $256.90  
  Purchase #5 $108.32   7.125%   $116.0378   $116.04   $116.05   $116.00  
  Purchase #6 $176.52   10.849%   $195.6707   $195.67   $195.65   $195.70  
  Purchase #7 $50.97   6.873%   $54.4732   $54.47   $54.45   $54.50  
  7 purchase totals = $947.63       $1,020.7402   $1,020.73   $1,020.75   $1,020.80