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 $93.96   10.836%   $104.1415   $104.14   $104.15   $104.10  
  Purchase #2 $54.70   9.612%   $59.9578   $59.96   $59.95   $60.00  
  Purchase #3 $162.28   8.539%   $176.1371   $176.14   $176.15   $176.10  
  Purchase #4 $109.36   7.863%   $117.959   $117.96   $117.95   $118.00  
  Purchase #5 $190.78   4.248%   $198.8843   $198.88   $198.90   $198.90  
  Purchase #6 $68.91   6.242%   $73.2114   $73.21   $73.20   $73.20  
  Purchase #7 $171.29   7.393%   $183.9535   $183.95   $183.95   $184.00  
  7 purchase totals = $851.28       $914.2446   $914.24   $914.25   $914.30