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	$47.29	9.356%	$51.7145	$51.71	$51.70	$51.70
Purchase #2	$36.30	3.330%	$37.5088	$37.51	$37.50	$37.50
Purchase #3	$228.38	9.800%	$250.7612	$250.76	$250.75	$250.80
Purchase #4	$164.86	13.321%	$186.821	$186.82	$186.80	$186.80
Purchase #5	$78.46	3.867%	$81.494	$81.49	$81.50	$81.50
Purchase #6	$187.68	11.418%	$209.1093	$209.11	$209.10	$209.10
Purchase #7	$156.96	12.627%	$176.7793	$176.78	$176.80	$176.80
7 purchase totals =	$899.93		$994.1881	$994.18	$994.15	$994.20