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 $64.27   4.637%   $67.2502   $67.25   $67.25   $67.30  
  Purchase #2 $107.91   11.453%   $120.2689   $120.27   $120.25   $120.30  
  Purchase #3 $110.32   13.307%   $125.0003   $125.00   $125.00   $125.00  
  Purchase #4 $192.91   6.230%   $204.9283   $204.93   $204.95   $204.90  
  Purchase #5 $136.80   3.707%   $141.8712   $141.87   $141.85   $141.90  
  Purchase #6 $118.71   4.821%   $124.433   $124.43   $124.45   $124.40  
  Purchase #7 $19.59   3.273%   $20.2312   $20.23   $20.25   $20.20  
  7 purchase totals = $750.51       $803.9831   $803.98   $804.00   $804.00