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 $238.65   9.737%   $261.8874   $261.89   $261.90   $261.90  
  Purchase #2 $98.66   6.333%   $104.9081   $104.91   $104.90   $104.90  
  Purchase #3 $40.25   9.313%   $43.9985   $44.00   $44.00   $44.00  
  Purchase #4 $202.92   5.309%   $213.693   $213.69   $213.70   $213.70  
  Purchase #5 $22.68   7.603%   $24.4044   $24.40   $24.40   $24.40  
  Purchase #6 $59.45   10.743%   $65.8367   $65.84   $65.85   $65.80  
  Purchase #7 $153.45   9.408%   $167.8866   $167.89   $167.90   $167.90  
  7 purchase totals = $816.06       $882.6147   $882.62   $882.65   $882.60