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	$201.47	11.870%	$225.3845	$225.38	$225.40	$225.40
Purchase #2	$93.34	7.693%	$100.5206	$100.52	$100.50	$100.50
Purchase #3	$66.64	7.243%	$71.4667	$71.47	$71.45	$71.50
Purchase #4	$209.44	12.650%	$235.9342	$235.93	$235.95	$235.90
Purchase #5	$26.77	9.305%	$29.2609	$29.26	$29.25	$29.30
Purchase #6	$60.87	10.814%	$67.4525	$67.45	$67.45	$67.50
Purchase #7	$33.52	7.560%	$36.0541	$36.05	$36.05	$36.10
7 purchase totals =	$692.05		$766.0735	$766.06	$766.05	$766.20