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 $106.98   11.344%   $119.1158   $119.12   $119.10   $119.10  
  Purchase #2 $213.26   8.630%   $231.6643   $231.66   $231.65   $231.70  
  Purchase #3 $112.72   10.577%   $124.6424   $124.64   $124.65   $124.60  
  Purchase #4 $207.74   4.677%   $217.456   $217.46   $217.45   $217.50  
  Purchase #5 $33.99   13.779%   $38.6735   $38.67   $38.65   $38.70  
  Purchase #6 $12.70   12.577%   $14.2973   $14.30   $14.30   $14.30  
  Purchase #7 $204.92   8.277%   $221.8812   $221.88   $221.90   $221.90  
  7 purchase totals = $892.31       $967.7305   $967.73   $967.70   $967.80