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 $14.58   11.787%   $16.2985   $16.30   $16.30   $16.30  
  Purchase #2 $135.99   11.117%   $151.108   $151.11   $151.10   $151.10  
  Purchase #3 $67.57   7.707%   $72.7776   $72.78   $72.80   $72.80  
  Purchase #4 $35.68   5.266%   $37.5589   $37.56   $37.55   $37.60  
  Purchase #5 $67.67   12.851%   $76.3663   $76.37   $76.35   $76.40  
  Purchase #6 $237.29   3.499%   $245.5928   $245.59   $245.60   $245.60  
  Purchase #7 $235.53   11.440%   $262.4746   $262.47   $262.45   $262.50  
  7 purchase totals = $794.31       $862.1767   $862.18   $862.15   $862.30