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 $206.93   10.146%   $227.9251   $227.93   $227.95   $227.90  
  Purchase #2 $60.85   13.849%   $69.2771   $69.28   $69.30   $69.30  
  Purchase #3 $133.80   8.578%   $145.2774   $145.28   $145.30   $145.30  
  Purchase #4 $30.40   8.719%   $33.0506   $33.05   $33.05   $33.10  
  Purchase #5 $229.50   5.181%   $241.3904   $241.39   $241.40   $241.40  
  Purchase #6 $74.76   8.812%   $81.3479   $81.35   $81.35   $81.30  
  Purchase #7 $236.78   3.804%   $245.7871   $245.79   $245.80   $245.80  
  7 purchase totals = $973.02       $1,044.0556   $1,044.07   $1,044.15   $1,044.10