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 $239.49   4.764%   $250.8993   $250.90   $250.90   $250.90  
  Purchase #2 $56.85   3.749%   $58.9813   $58.98   $59.00   $59.00  
  Purchase #3 $221.76   5.241%   $233.3824   $233.38   $233.40   $233.40  
  Purchase #4 $126.93   9.560%   $139.0645   $139.06   $139.05   $139.10  
  Purchase #5 $218.56   11.497%   $243.6878   $243.69   $243.70   $243.70  
  Purchase #6 $244.45   9.738%   $268.2545   $268.25   $268.25   $268.30  
  Purchase #7 $120.63   11.393%   $134.3734   $134.37   $134.35   $134.40  
  7 purchase totals = $1,228.67       $1,328.6432   $1,328.63   $1,328.65   $1,328.80