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 $143.25   5.565%   $151.2219   $151.22   $151.20   $151.20  
  Purchase #2 $130.76   7.288%   $140.2898   $140.29   $140.30   $140.30  
  Purchase #3 $183.95   12.844%   $207.5765   $207.58   $207.60   $207.60  
  Purchase #4 $58.48   12.689%   $65.9005   $65.90   $65.90   $65.90  
  Purchase #5 $75.36   11.460%   $83.9963   $84.00   $84.00   $84.00  
  Purchase #6 $239.63   5.873%   $253.7035   $253.70   $253.70   $253.70  
  Purchase #7 $97.96   13.865%   $111.5422   $111.54   $111.55   $111.50  
  7 purchase totals = $929.39       $1,014.2307   $1,014.23   $1,014.25   $1,014.20