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 $176.86   4.828%   $185.3988   $185.40   $185.40   $185.40  
  Purchase #2 $237.79   5.224%   $250.2121   $250.21   $250.20   $250.20  
  Purchase #3 $19.83   3.328%   $20.4899   $20.49   $20.50   $20.50  
  Purchase #4 $139.68   4.220%   $145.5745   $145.57   $145.55   $145.60  
  Purchase #5 $81.72   3.293%   $84.411   $84.41   $84.40   $84.40  
  Purchase #6 $89.61   4.635%   $93.7634   $93.76   $93.75   $93.80  
  Purchase #7 $226.30   7.225%   $242.6502   $242.65   $242.65   $242.70  
  7 purchase totals = $971.79       $1,022.4999   $1,022.49   $1,022.45   $1,022.60