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 $226.34   13.511%   $256.9208   $256.92   $256.90   $256.90  
  Purchase #2 $216.80   10.466%   $239.4903   $239.49   $239.50   $239.50  
  Purchase #3 $175.96   12.493%   $197.9427   $197.94   $197.95   $197.90  
  Purchase #4 $246.91   3.104%   $254.5741   $254.57   $254.55   $254.60  
  Purchase #5 $213.91   11.703%   $238.9439   $238.94   $238.95   $238.90  
  Purchase #6 $189.35   9.239%   $206.844   $206.84   $206.85   $206.80  
  Purchase #7 $102.69   3.797%   $106.5891   $106.59   $106.60   $106.60  
  7 purchase totals = $1,371.96       $1,501.3049   $1,501.29   $1,501.30   $1,501.20