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 $185.91   13.468%   $210.9484   $210.95   $210.95   $210.90  
  Purchase #2 $119.68   4.427%   $124.9782   $124.98   $125.00   $125.00  
  Purchase #3 $11.90   5.662%   $12.5738   $12.57   $12.55   $12.60  
  Purchase #4 $23.49   12.837%   $26.5054   $26.51   $26.50   $26.50  
  Purchase #5 $192.90   6.402%   $205.2495   $205.25   $205.25   $205.20  
  Purchase #6 $11.71   4.853%   $12.2783   $12.28   $12.30   $12.30  
  Purchase #7 $227.30   11.818%   $254.1623   $254.16   $254.15   $254.20  
  7 purchase totals = $772.89       $846.6959   $846.70   $846.70   $846.70