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 $44.87   3.709%   $46.5342   $46.53   $46.55   $46.50  
  Purchase #2 $159.67   6.194%   $169.56   $169.56   $169.55   $169.60  
  Purchase #3 $48.51   7.211%   $52.0081   $52.01   $52.00   $52.00  
  Purchase #4 $106.76   12.109%   $119.6876   $119.69   $119.70   $119.70  
  Purchase #5 $180.26   4.492%   $188.3573   $188.36   $188.35   $188.40  
  Purchase #6 $204.72   10.185%   $225.5707   $225.57   $225.55   $225.60  
  Purchase #7 $12.91   8.482%   $14.005   $14.01   $14.00   $14.00  
  7 purchase totals = $757.70       $815.7229   $815.73   $815.70   $815.80