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 $63.95   6.383%   $68.0319   $68.03   $68.05   $68.00  
  Purchase #2 $225.32   13.861%   $256.5516   $256.55   $256.55   $256.60  
  Purchase #3 $115.34   9.213%   $125.9663   $125.97   $125.95   $126.00  
  Purchase #4 $193.30   7.405%   $207.6139   $207.61   $207.60   $207.60  
  Purchase #5 $203.32   11.326%   $226.348   $226.35   $226.35   $226.30  
  Purchase #6 $80.89   5.297%   $85.1747   $85.17   $85.15   $85.20  
  Purchase #7 $12.31   3.693%   $12.7646   $12.76   $12.75   $12.80  
  7 purchase totals = $894.43       $982.4510   $982.44   $982.40   $982.50