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 $239.86   13.527%   $272.3059   $272.31   $272.30   $272.30  
  Purchase #2 $42.34   8.765%   $46.0511   $46.05   $46.05   $46.10  
  Purchase #3 $54.51   11.572%   $60.8179   $60.82   $60.80   $60.80  
  Purchase #4 $183.72   6.617%   $195.8768   $195.88   $195.90   $195.90  
  Purchase #5 $229.37   11.639%   $256.0664   $256.07   $256.05   $256.10  
  Purchase #6 $111.87   5.647%   $118.1873   $118.19   $118.20   $118.20  
  Purchase #7 $192.72   5.547%   $203.4102   $203.41   $203.40   $203.40  
  7 purchase totals = $1,054.39       $1,152.7156   $1,152.73   $1,152.70   $1,152.80