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 $226.86   11.358%   $252.6268   $252.63   $252.65   $252.60  
  Purchase #2 $116.48   11.304%   $129.6469   $129.65   $129.65   $129.60  
  Purchase #3 $31.71   3.817%   $32.9204   $32.92   $32.90   $32.90  
  Purchase #4 $42.29   11.802%   $47.2811   $47.28   $47.30   $47.30  
  Purchase #5 $178.67   7.701%   $192.4294   $192.43   $192.45   $192.40  
  Purchase #6 $141.51   11.288%   $157.4836   $157.48   $157.50   $157.50  
  Purchase #7 $116.31   7.273%   $124.7692   $124.77   $124.75   $124.80  
  7 purchase totals = $853.83       $937.1574   $937.16   $937.20   $937.10