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 $215.86   4.720%   $226.0486   $226.05   $226.05   $226.00  
  Purchase #2 $127.58   3.321%   $131.8169   $131.82   $131.80   $131.80  
  Purchase #3 $68.99   13.480%   $78.2899   $78.29   $78.30   $78.30  
  Purchase #4 $91.37   10.719%   $101.164   $101.16   $101.15   $101.20  
  Purchase #5 $232.55   7.777%   $250.6354   $250.64   $250.65   $250.60  
  Purchase #6 $41.25   5.647%   $43.5794   $43.58   $43.60   $43.60  
  Purchase #7 $197.97   13.307%   $224.3139   $224.31   $224.30   $224.30  
  7 purchase totals = $975.57       $1,055.8481   $1,055.85   $1,055.85   $1,055.80