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	$10.56	3.502%	$10.9298	$10.93	$10.95	$10.90
Purchase #2	$131.44	13.251%	$148.8571	$148.86	$148.85	$148.90
Purchase #3	$82.27	9.483%	$90.0717	$90.07	$90.05	$90.10
Purchase #4	$90.72	5.583%	$95.7849	$95.78	$95.80	$95.80
Purchase #5	$155.61	3.153%	$160.5164	$160.52	$160.50	$160.50
Purchase #6	$67.69	10.774%	$74.9829	$74.98	$75.00	$75.00
Purchase #7	$46.99	7.254%	$50.3987	$50.40	$50.40	$50.40
7 purchase totals =	$585.28		$631.5415	$631.54	$631.55	$631.60