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 $24.76   6.390%   $26.3422   $26.34   $26.35   $26.30  
  Purchase #2 $250.79   3.398%   $259.3118   $259.31   $259.30   $259.30  
  Purchase #3 $208.69   8.855%   $227.1695   $227.17   $227.15   $227.20  
  Purchase #4 $116.29   11.177%   $129.2877   $129.29   $129.30   $129.30  
  Purchase #5 $123.45   8.261%   $133.6482   $133.65   $133.65   $133.60  
  Purchase #6 $30.66   6.848%   $32.7596   $32.76   $32.75   $32.80  
  Purchase #7 $179.49   13.381%   $203.5076   $203.51   $203.50   $203.50  
  7 purchase totals = $934.13       $1,012.0266   $1,012.03   $1,012.00   $1,012.00