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 $63.86   8.295%   $69.1572   $69.16   $69.15   $69.20  
  Purchase #2 $226.51   10.370%   $249.9991   $250.00   $250.00   $250.00  
  Purchase #3 $91.35   10.574%   $101.0093   $101.01   $101.00   $101.00  
  Purchase #4 $13.29   11.399%   $14.8049   $14.80   $14.80   $14.80  
  Purchase #5 $216.38   4.297%   $225.6778   $225.68   $225.70   $225.70  
  Purchase #6 $224.33   9.129%   $244.8091   $244.81   $244.80   $244.80  
  Purchase #7 $23.95   3.694%   $24.8347   $24.83   $24.85   $24.80  
  7 purchase totals = $859.67       $930.2921   $930.29   $930.30   $930.30