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 $112.77   11.787%   $126.0622   $126.06   $126.05   $126.10  
  Purchase #2 $98.38   3.557%   $101.8794   $101.88   $101.90   $101.90  
  Purchase #3 $83.99   6.364%   $89.3351   $89.34   $89.35   $89.30  
  Purchase #4 $42.99   5.729%   $45.4529   $45.45   $45.45   $45.50  
  Purchase #5 $244.39   6.670%   $260.6908   $260.69   $260.70   $260.70  
  Purchase #6 $76.40   3.547%   $79.1099   $79.11   $79.10   $79.10  
  Purchase #7 $196.51   6.487%   $209.2576   $209.26   $209.25   $209.30  
  7 purchase totals = $855.43       $911.7879   $911.79   $911.80   $911.90