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 $41.33   5.755%   $43.7085   $43.71   $43.70   $43.70  
  Purchase #2 $186.43   9.133%   $203.4567   $203.46   $203.45   $203.50  
  Purchase #3 $124.70   3.757%   $129.385   $129.39   $129.40   $129.40  
  Purchase #4 $202.82   3.505%   $209.9288   $209.93   $209.95   $209.90  
  Purchase #5 $103.54   13.736%   $117.7623   $117.76   $117.75   $117.80  
  Purchase #6 $67.69   13.632%   $76.9175   $76.92   $76.90   $76.90  
  Purchase #7 $90.42   5.238%   $95.1562   $95.16   $95.15   $95.20  
  7 purchase totals = $816.93       $876.3150   $876.33   $876.30   $876.40