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	$40.76	11.678%	$45.52	$45.52	$45.50	$45.50
Purchase #2	$64.88	4.677%	$67.9144	$67.91	$67.90	$67.90
Purchase #3	$56.80	6.569%	$60.5312	$60.53	$60.55	$60.50
Purchase #4	$62.98	10.456%	$69.5652	$69.57	$69.55	$69.60
Purchase #5	$139.65	8.779%	$151.9099	$151.91	$151.90	$151.90
Purchase #6	$82.70	13.801%	$94.1134	$94.11	$94.10	$94.10
Purchase #7	$140.36	3.356%	$145.0705	$145.07	$145.05	$145.10
7 purchase totals =	$588.13		$634.6246	$634.62	$634.55	$634.60