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 $13.43   8.721%   $14.6012   $14.60   $14.60   $14.60  
  Purchase #2 $221.96   3.464%   $229.6487   $229.65   $229.65   $229.60  
  Purchase #3 $42.49   11.336%   $47.3067   $47.31   $47.30   $47.30  
  Purchase #4 $104.44   6.535%   $111.2652   $111.27   $111.25   $111.30  
  Purchase #5 $240.98   8.253%   $260.8681   $260.87   $260.85   $260.90  
  Purchase #6 $175.42   9.518%   $192.1165   $192.12   $192.10   $192.10  
  Purchase #7 $176.79   5.681%   $186.8334   $186.83   $186.85   $186.80  
  7 purchase totals = $975.51       $1,042.6398   $1,042.65   $1,042.60   $1,042.60