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	$112.74	13.399%	$127.846	$127.85	$127.85	$127.80
Purchase #2	$92.27	5.589%	$97.427	$97.43	$97.45	$97.40
Purchase #3	$191.37	13.794%	$217.7676	$217.77	$217.75	$217.80
Purchase #4	$113.34	3.605%	$117.4259	$117.43	$117.45	$117.40
Purchase #5	$102.85	7.579%	$110.645	$110.65	$110.65	$110.60
Purchase #6	$33.39	9.339%	$36.5083	$36.51	$36.50	$36.50
Purchase #7	$246.85	9.585%	$270.5106	$270.51	$270.50	$270.50
7 purchase totals =	$892.81		$978.1304	$978.15	$978.15	$978.00