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 $202.53   10.723%   $224.2473   $224.25   $224.25   $224.20  
  Purchase #2 $91.40   6.648%   $97.4763   $97.48   $97.50   $97.50  
  Purchase #3 $104.58   4.198%   $108.9703   $108.97   $108.95   $109.00  
  Purchase #4 $202.63   3.363%   $209.4444   $209.44   $209.45   $209.40  
  Purchase #5 $157.33   4.322%   $164.1298   $164.13   $164.15   $164.10  
  Purchase #6 $53.79   8.639%   $58.4369   $58.44   $58.45   $58.40  
  Purchase #7 $181.93   10.204%   $200.4941   $200.49   $200.50   $200.50  
  7 purchase totals = $994.19       $1,063.1991   $1,063.20   $1,063.25   $1,063.10