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	$42.30	8.230%	$45.7813	$45.78	$45.80	$45.80
Purchase #2	$99.52	12.361%	$111.8217	$111.82	$111.80	$111.80
Purchase #3	$60.70	11.625%	$67.7564	$67.76	$67.75	$67.80
Purchase #4	$41.36	10.206%	$45.5812	$45.58	$45.60	$45.60
Purchase #5	$210.53	10.397%	$232.4188	$232.42	$232.40	$232.40
Purchase #6	$67.46	11.200%	$75.0155	$75.02	$75.00	$75.00
Purchase #7	$59.55	12.477%	$66.9801	$66.98	$67.00	$67.00
7 purchase totals =	$581.42		$645.3550	$645.36	$645.35	$645.40