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 $128.79   9.129%   $140.5472   $140.55   $140.55   $140.50  
  Purchase #2 $37.65   12.869%   $42.4952   $42.50   $42.50   $42.50  
  Purchase #3 $143.81   9.424%   $157.3627   $157.36   $157.35   $157.40  
  Purchase #4 $51.71   3.514%   $53.5271   $53.53   $53.55   $53.50  
  Purchase #5 $13.28   5.411%   $13.9986   $14.00   $14.00   $14.00  
  Purchase #6 $106.84   9.468%   $116.9556   $116.96   $116.95   $117.00  
  Purchase #7 $97.91   12.707%   $110.3514   $110.35   $110.35   $110.40  
  7 purchase totals = $579.99       $635.2378   $635.25   $635.25   $635.30