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 $59.95   13.552%   $68.0744   $68.07   $68.05   $68.10  
  Purchase #2 $243.62   4.747%   $255.1846   $255.18   $255.20   $255.20  
  Purchase #3 $215.56   9.505%   $236.049   $236.05   $236.05   $236.00  
  Purchase #4 $107.63   9.518%   $117.8742   $117.87   $117.85   $117.90  
  Purchase #5 $89.48   6.543%   $95.3347   $95.33   $95.35   $95.30  
  Purchase #6 $222.81   3.357%   $230.2897   $230.29   $230.30   $230.30  
  Purchase #7 $92.92   8.384%   $100.7104   $100.71   $100.70   $100.70  
  7 purchase totals = $1,031.97       $1,103.5170   $1,103.50   $1,103.50   $1,103.50