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	$80.76	12.343%	$90.7282	$90.73	$90.75	$90.70
Purchase #2	$185.50	13.446%	$210.4423	$210.44	$210.45	$210.40
Purchase #3	$112.47	13.319%	$127.4499	$127.45	$127.45	$127.40
Purchase #4	$174.78	4.823%	$183.2096	$183.21	$183.20	$183.20
Purchase #5	$175.61	13.600%	$199.493	$199.49	$199.50	$199.50
Purchase #6	$220.90	3.296%	$228.1809	$228.18	$228.20	$228.20
Purchase #7	$209.33	8.145%	$226.3799	$226.38	$226.40	$226.40
7 purchase totals =	$1,159.35		$1,265.8838	$1,265.88	$1,265.95	$1,265.80