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 $18.48   6.485%   $19.6784   $19.68   $19.70   $19.70  
  Purchase #2 $222.53   4.765%   $233.1336   $233.13   $233.15   $233.10  
  Purchase #3 $112.26   6.437%   $119.4862   $119.49   $119.50   $119.50  
  Purchase #4 $225.75   7.538%   $242.767   $242.77   $242.75   $242.80  
  Purchase #5 $48.30   9.765%   $53.0165   $53.02   $53.00   $53.00  
  Purchase #6 $52.75   13.659%   $59.9551   $59.96   $59.95   $60.00  
  Purchase #7 $52.39   6.868%   $55.9881   $55.99   $56.00   $56.00  
  7 purchase totals = $732.46       $784.0249   $784.04   $784.05   $784.10