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	$16.29	10.484%	$17.9978	$18.00	$18.00	$18.00
Purchase #2	$105.62	4.783%	$110.6718	$110.67	$110.65	$110.70
Purchase #3	$56.32	5.263%	$59.2841	$59.28	$59.30	$59.30
Purchase #4	$90.41	11.129%	$100.4717	$100.47	$100.45	$100.50
Purchase #5	$166.99	12.816%	$188.3914	$188.39	$188.40	$188.40
Purchase #6	$211.35	6.692%	$225.4935	$225.49	$225.50	$225.50
Purchase #7	$232.30	4.415%	$242.556	$242.56	$242.55	$242.60
7 purchase totals =	$879.28		$944.8663	$944.86	$944.85	$945.00