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 $248.60   8.146%   $268.851   $268.85   $268.85   $268.90  
  Purchase #2 $211.78   13.496%   $240.3618   $240.36   $240.35   $240.40  
  Purchase #3 $32.27   6.859%   $34.4834   $34.48   $34.50   $34.50  
  Purchase #4 $186.61   3.193%   $192.5685   $192.57   $192.55   $192.60  
  Purchase #5 $101.55   5.579%   $107.2155   $107.22   $107.20   $107.20  
  Purchase #6 $86.76   5.541%   $91.5674   $91.57   $91.55   $91.60  
  Purchase #7 $5.31   10.344%   $5.8593   $5.86   $5.85   $5.90  
  7 purchase totals = $872.88       $940.9069   $940.91   $940.85   $941.10