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	$82.48	7.160%	$88.3856	$88.39	$88.40	$88.40
Purchase #2	$90.78	9.283%	$99.2071	$99.21	$99.20	$99.20
Purchase #3	$142.69	7.580%	$153.5059	$153.51	$153.50	$153.50
Purchase #4	$94.43	10.626%	$104.4641	$104.46	$104.45	$104.50
Purchase #5	$56.36	6.520%	$60.0347	$60.03	$60.05	$60.00
Purchase #6	$124.47	3.740%	$129.1252	$129.13	$129.15	$129.10
Purchase #7	$86.75	11.691%	$96.8919	$96.89	$96.90	$96.90
7 purchase totals =	$677.96		$731.6145	$731.62	$731.65	$731.60