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 $88.29   6.417%   $93.9556   $93.96   $93.95   $94.00  
  Purchase #2 $27.71   9.246%   $30.2721   $30.27   $30.25   $30.30  
  Purchase #3 $109.62   6.858%   $117.1377   $117.14   $117.15   $117.10  
  Purchase #4 $6.34   3.277%   $6.5478   $6.55   $6.55   $6.50  
  Purchase #5 $83.79   11.280%   $93.2415   $93.24   $93.25   $93.20  
  Purchase #6 $106.49   12.217%   $119.4999   $119.50   $119.50   $119.50  
  Purchase #7 $116.35   12.542%   $130.9426   $130.94   $130.95   $130.90  
  7 purchase totals = $538.59       $591.5972   $591.60   $591.60   $591.50