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	$18.42	8.834%	$20.0472	$20.05	$20.05	$20.00
Purchase #2	$211.41	5.704%	$223.4688	$223.47	$223.45	$223.50
Purchase #3	$89.53	7.757%	$96.4748	$96.47	$96.45	$96.50
Purchase #4	$221.49	3.764%	$229.8269	$229.83	$229.85	$229.80
Purchase #5	$33.74	10.870%	$37.4075	$37.41	$37.40	$37.40
Purchase #6	$43.75	12.209%	$49.0914	$49.09	$49.10	$49.10
Purchase #7	$71.27	5.638%	$75.2882	$75.29	$75.30	$75.30
7 purchase totals =	$689.61		$731.6048	$731.61	$731.60	$731.60