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	$82.49	12.188%	$92.5439	$92.54	$92.55	$92.50
Purchase #2	$37.77	12.166%	$42.3651	$42.37	$42.35	$42.40
Purchase #3	$210.65	8.486%	$228.5258	$228.53	$228.55	$228.50
Purchase #4	$30.76	13.501%	$34.9129	$34.91	$34.90	$34.90
Purchase #5	$112.46	13.679%	$127.8434	$127.84	$127.85	$127.80
Purchase #6	$80.58	12.278%	$90.4736	$90.47	$90.45	$90.50
Purchase #7	$189.82	4.589%	$198.5308	$198.53	$198.55	$198.50
7 purchase totals =	$744.53		$815.1955	$815.19	$815.20	$815.10