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	$172.83	8.388%	$187.327	$187.33	$187.35	$187.30
Purchase #2	$189.90	12.504%	$213.6451	$213.65	$213.65	$213.60
Purchase #3	$5.74	4.370%	$5.9908	$5.99	$6.00	$6.00
Purchase #4	$65.88	10.112%	$72.5418	$72.54	$72.55	$72.50
Purchase #5	$33.27	13.777%	$37.8536	$37.85	$37.85	$37.90
Purchase #6	$108.89	7.862%	$117.4509	$117.45	$117.45	$117.50
Purchase #7	$181.96	5.359%	$191.7112	$191.71	$191.70	$191.70
7 purchase totals =	$758.47		$826.5204	$826.52	$826.55	$826.50