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 $60.46   4.282%   $63.0489   $63.05   $63.05   $63.00  
  Purchase #2 $12.99   13.502%   $14.7439   $14.74   $14.75   $14.70  
  Purchase #3 $55.39   9.831%   $60.8354   $60.84   $60.85   $60.80  
  Purchase #4 $229.96   10.703%   $254.5726   $254.57   $254.55   $254.60  
  Purchase #5 $246.62   7.233%   $264.458   $264.46   $264.45   $264.50  
  Purchase #6 $179.66   3.257%   $185.5115   $185.51   $185.50   $185.50  
  Purchase #7 $132.88   11.648%   $148.3579   $148.36   $148.35   $148.40  
  7 purchase totals = $917.96       $991.5282   $991.53   $991.50   $991.50