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 $41.53   4.132%   $43.246   $43.25   $43.25   $43.20  
  Purchase #2 $16.74   9.214%   $18.2824   $18.28   $18.30   $18.30  
  Purchase #3 $46.43   7.207%   $49.7762   $49.78   $49.80   $49.80  
  Purchase #4 $233.27   8.249%   $252.5124   $252.51   $252.50   $252.50  
  Purchase #5 $107.35   11.410%   $119.5986   $119.60   $119.60   $119.60  
  Purchase #6 $249.31   9.420%   $272.795   $272.80   $272.80   $272.80  
  Purchase #7 $186.46   12.188%   $209.1857   $209.19   $209.20   $209.20  
  7 purchase totals = $881.09       $965.3963   $965.41   $965.45   $965.40