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	$176.46	7.494%	$189.6839	$189.68	$189.70	$189.70
Purchase #2	$124.98	10.699%	$138.3516	$138.35	$138.35	$138.40
Purchase #3	$80.89	6.233%	$85.9319	$85.93	$85.95	$85.90
Purchase #4	$100.41	4.802%	$105.2317	$105.23	$105.25	$105.20
Purchase #5	$77.89	4.559%	$81.441	$81.44	$81.45	$81.40
Purchase #6	$68.27	5.238%	$71.846	$71.85	$71.85	$71.80
Purchase #7	$64.73	4.143%	$67.4118	$67.41	$67.40	$67.40
7 purchase totals =	$693.63		$739.8979	$739.89	$739.95	$739.80