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	$28.64	11.352%	$31.8912	$31.89	$31.90	$31.90
Purchase #2	$175.74	5.342%	$185.128	$185.13	$185.15	$185.10
Purchase #3	$127.74	4.340%	$133.2839	$133.28	$133.30	$133.30
Purchase #4	$119.54	9.492%	$130.8867	$130.89	$130.90	$130.90
Purchase #5	$244.67	10.180%	$269.5774	$269.58	$269.60	$269.60
Purchase #6	$52.46	4.390%	$54.763	$54.76	$54.75	$54.80
Purchase #7	$93.82	7.358%	$100.7233	$100.72	$100.70	$100.70
7 purchase totals =	$842.61		$906.2535	$906.25	$906.30	$906.30