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 $119.47   6.652%   $127.4171   $127.42   $127.40   $127.40  
  Purchase #2 $86.57   11.593%   $96.6061   $96.61   $96.60   $96.60  
  Purchase #3 $43.91   9.638%   $48.142   $48.14   $48.15   $48.10  
  Purchase #4 $95.82   7.799%   $103.293   $103.29   $103.30   $103.30  
  Purchase #5 $218.40   8.525%   $237.0186   $237.02   $237.00   $237.00  
  Purchase #6 $52.27   9.359%   $57.1619   $57.16   $57.15   $57.20  
  Purchase #7 $140.41   9.289%   $153.4527   $153.45   $153.45   $153.50  
  7 purchase totals = $756.85       $823.0914   $823.09   $823.05   $823.10