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 $191.25   13.647%   $217.3499   $217.35   $217.35   $217.30  
  Purchase #2 $205.86   8.198%   $222.7364   $222.74   $222.75   $222.70  
  Purchase #3 $153.35   3.859%   $159.2678   $159.27   $159.25   $159.30  
  Purchase #4 $200.52   4.496%   $209.5354   $209.54   $209.55   $209.50  
  Purchase #5 $134.76   8.427%   $146.1162   $146.12   $146.10   $146.10  
  Purchase #6 $46.76   5.828%   $49.4852   $49.49   $49.50   $49.50  
  Purchase #7 $55.93   8.654%   $60.7702   $60.77   $60.75   $60.80  
  7 purchase totals = $988.43       $1,065.2611   $1,065.28   $1,065.25   $1,065.20