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 $69.27   8.730%   $75.3173   $75.32   $75.30   $75.30  
  Purchase #2 $219.87   7.365%   $236.0634   $236.06   $236.05   $236.10  
  Purchase #3 $36.62   8.603%   $39.7704   $39.77   $39.75   $39.80  
  Purchase #4 $203.28   11.160%   $225.966   $225.97   $225.95   $226.00  
  Purchase #5 $215.34   11.783%   $240.7135   $240.71   $240.70   $240.70  
  Purchase #6 $79.62   9.447%   $87.1417   $87.14   $87.15   $87.10  
  Purchase #7 $7.68   10.214%   $8.4644   $8.46   $8.45   $8.50  
  7 purchase totals = $831.68       $913.4367   $913.43   $913.35   $913.50