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 $197.26   6.564%   $210.2081   $210.21   $210.20   $210.20  
  Purchase #2 $119.46   4.320%   $124.6207   $124.62   $124.60   $124.60  
  Purchase #3 $25.66   9.161%   $28.0107   $28.01   $28.00   $28.00  
  Purchase #4 $59.46   6.414%   $63.2738   $63.27   $63.25   $63.30  
  Purchase #5 $54.49   6.196%   $57.8662   $57.87   $57.85   $57.90  
  Purchase #6 $200.88   8.303%   $217.5591   $217.56   $217.55   $217.60  
  Purchase #7 $202.36   6.702%   $215.9222   $215.92   $215.90   $215.90  
  7 purchase totals = $859.57       $917.4608   $917.46   $917.35   $917.50