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 $88.90   9.533%   $97.3748   $97.37   $97.35   $97.40  
  Purchase #2 $228.49   9.377%   $249.9155   $249.92   $249.90   $249.90  
  Purchase #3 $8.35   5.646%   $8.8214   $8.82   $8.80   $8.80  
  Purchase #4 $181.47   5.716%   $191.8428   $191.84   $191.85   $191.80  
  Purchase #5 $83.29   3.166%   $85.927   $85.93   $85.95   $85.90  
  Purchase #6 $193.76   3.426%   $200.3982   $200.40   $200.40   $200.40  
  Purchase #7 $104.36   4.860%   $109.4319   $109.43   $109.45   $109.40  
  7 purchase totals = $888.62       $943.7116   $943.71   $943.70   $943.60