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	$27.57	6.588%	$29.3863	$29.39	$29.40	$29.40
Purchase #2	$198.97	7.369%	$213.6321	$213.63	$213.65	$213.60
Purchase #3	$100.33	12.517%	$112.8883	$112.89	$112.90	$112.90
Purchase #4	$189.25	3.624%	$196.1084	$196.11	$196.10	$196.10
Purchase #5	$153.35	4.177%	$159.7554	$159.76	$159.75	$159.80
Purchase #6	$188.33	10.292%	$207.7129	$207.71	$207.70	$207.70
Purchase #7	$149.54	11.707%	$167.0466	$167.05	$167.05	$167.00
7 purchase totals =	$1,007.34		$1,086.5300	$1,086.54	$1,086.55	$1,086.50