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 $189.29   7.669%   $203.8067   $203.81   $203.80   $203.80  
  Purchase #2 $117.30   6.788%   $125.2623   $125.26   $125.25   $125.30  
  Purchase #3 $245.41   8.486%   $266.2355   $266.24   $266.25   $266.20  
  Purchase #4 $226.89   13.501%   $257.5224   $257.52   $257.50   $257.50  
  Purchase #5 $125.85   3.211%   $129.891   $129.89   $129.90   $129.90  
  Purchase #6 $184.83   10.120%   $203.5348   $203.53   $203.55   $203.50  
  Purchase #7 $104.95   11.507%   $117.0266   $117.03   $117.05   $117.00  
  7 purchase totals = $1,194.52       $1,303.2793   $1,303.28   $1,303.30   $1,303.20