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 $63.43   3.242%   $65.4864   $65.49   $65.50   $65.50  
  Purchase #2 $249.31   3.376%   $257.7267   $257.73   $257.75   $257.70  
  Purchase #3 $165.36   3.841%   $171.7115   $171.71   $171.70   $171.70  
  Purchase #4 $17.85   8.278%   $19.3276   $19.33   $19.35   $19.30  
  Purchase #5 $244.39   13.269%   $276.8181   $276.82   $276.80   $276.80  
  Purchase #6 $236.55   7.265%   $253.7354   $253.74   $253.75   $253.70  
  Purchase #7 $209.47   4.212%   $218.2929   $218.29   $218.30   $218.30  
  7 purchase totals = $1,186.36       $1,263.0986   $1,263.11   $1,263.15   $1,263.00