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	$89.65	6.664%	$95.6243	$95.62	$95.60	$95.60
Purchase #2	$77.84	13.741%	$88.536	$88.54	$88.55	$88.50
Purchase #3	$53.33	8.679%	$57.9585	$57.96	$57.95	$58.00
Purchase #4	$43.73	4.213%	$45.5723	$45.57	$45.55	$45.60
Purchase #5	$74.32	11.743%	$83.0474	$83.05	$83.05	$83.00
Purchase #6	$86.94	4.152%	$90.5497	$90.55	$90.55	$90.50
Purchase #7	$187.88	4.220%	$195.8085	$195.81	$195.80	$195.80
7 purchase totals =	$613.69		$657.0967	$657.10	$657.05	$657.00