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 $128.27   9.429%   $140.3646   $140.36   $140.35   $140.40  
  Purchase #2 $96.35   6.186%   $102.3102   $102.31   $102.30   $102.30  
  Purchase #3 $120.57   4.164%   $125.5905   $125.59   $125.60   $125.60  
  Purchase #4 $161.89   7.141%   $173.4506   $173.45   $173.45   $173.50  
  Purchase #5 $206.41   3.151%   $212.914   $212.91   $212.90   $212.90  
  Purchase #6 $55.50   8.558%   $60.2497   $60.25   $60.25   $60.20  
  Purchase #7 $57.71   3.569%   $59.7697   $59.77   $59.75   $59.80  
  7 purchase totals = $826.70       $874.6493   $874.64   $874.60   $874.70