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 $32.49   11.702%   $36.292   $36.29   $36.30   $36.30  
  Purchase #2 $123.72   3.339%   $127.851   $127.85   $127.85   $127.90  
  Purchase #3 $154.37   10.757%   $170.9756   $170.98   $171.00   $171.00  
  Purchase #4 $62.70   3.596%   $64.9547   $64.95   $64.95   $65.00  
  Purchase #5 $66.37   13.371%   $75.2443   $75.24   $75.25   $75.20  
  Purchase #6 $179.45   10.800%   $198.8306   $198.83   $198.85   $198.80  
  Purchase #7 $93.53   3.105%   $96.4341   $96.43   $96.45   $96.40  
  7 purchase totals = $712.63       $770.5823   $770.57   $770.65   $770.60