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 $58.55   8.520%   $63.5385   $63.54   $63.55   $63.50  
  Purchase #2 $148.54   7.592%   $159.8172   $159.82   $159.80   $159.80  
  Purchase #3 $230.97   11.281%   $257.0257   $257.03   $257.05   $257.00  
  Purchase #4 $178.83   5.542%   $188.7408   $188.74   $188.75   $188.70  
  Purchase #5 $32.30   7.671%   $34.7777   $34.78   $34.80   $34.80  
  Purchase #6 $26.28   13.722%   $29.8861   $29.89   $29.90   $29.90  
  Purchase #7 $21.31   3.498%   $22.0554   $22.06   $22.05   $22.10  
  7 purchase totals = $696.78       $755.8414   $755.86   $755.90   $755.80