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	$32.83	8.339%	$35.5677	$35.57	$35.55	$35.60
Purchase #2	$46.47	13.871%	$52.9159	$52.92	$52.90	$52.90
Purchase #3	$92.43	8.608%	$100.3864	$100.39	$100.40	$100.40
Purchase #4	$42.79	6.723%	$45.6668	$45.67	$45.65	$45.70
Purchase #5	$110.93	9.470%	$121.4351	$121.44	$121.45	$121.40
Purchase #6	$89.47	9.609%	$98.0672	$98.07	$98.05	$98.10
Purchase #7	$56.38	7.357%	$60.5279	$60.53	$60.55	$60.50
7 purchase totals =	$471.30		$514.5670	$514.59	$514.55	$514.60