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 $104.72   8.259%   $113.3688   $113.37   $113.35   $113.40  
  Purchase #2 $185.43   3.624%   $192.15   $192.15   $192.15   $192.20  
  Purchase #3 $202.63   7.363%   $217.5496   $217.55   $217.55   $217.50  
  Purchase #4 $141.87   9.452%   $155.2796   $155.28   $155.30   $155.30  
  Purchase #5 $152.67   5.779%   $161.4928   $161.49   $161.50   $161.50  
  Purchase #6 $200.99   4.731%   $210.4988   $210.50   $210.50   $210.50  
  Purchase #7 $103.37   5.854%   $109.4213   $109.42   $109.40   $109.40  
  7 purchase totals = $1,091.68       $1,159.7609   $1,159.76   $1,159.75   $1,159.80