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	$91.40	8.352%	$99.0337	$99.03	$99.05	$99.00
Purchase #2	$29.87	7.606%	$32.1419	$32.14	$32.15	$32.10
Purchase #3	$160.62	12.300%	$180.3763	$180.38	$180.40	$180.40
Purchase #4	$48.89	11.446%	$54.4859	$54.49	$54.50	$54.50
Purchase #5	$57.84	8.582%	$62.8038	$62.80	$62.80	$62.80
Purchase #6	$247.68	6.611%	$264.0541	$264.05	$264.05	$264.10
Purchase #7	$110.73	7.808%	$119.3758	$119.38	$119.40	$119.40
7 purchase totals =	$747.03		$812.2715	$812.27	$812.35	$812.30