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 $111.66   13.161%   $126.3556   $126.36   $126.35   $126.40  
  Purchase #2 $163.78   7.654%   $176.3157   $176.32   $176.30   $176.30  
  Purchase #3 $230.62   13.687%   $262.185   $262.19   $262.20   $262.20  
  Purchase #4 $96.94   6.617%   $103.3545   $103.35   $103.35   $103.40  
  Purchase #5 $152.71   4.202%   $159.1269   $159.13   $159.15   $159.10  
  Purchase #6 $162.50   12.717%   $183.1651   $183.17   $183.15   $183.20  
  Purchase #7 $134.55   8.643%   $146.1792   $146.18   $146.20   $146.20  
  7 purchase totals = $1,052.76       $1,156.6820   $1,156.70   $1,156.70   $1,156.80