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	$83.65	8.173%	$90.4867	$90.49	$90.50	$90.50
Purchase #2	$148.75	7.521%	$159.9375	$159.94	$159.95	$159.90
Purchase #3	$90.37	11.264%	$100.5493	$100.55	$100.55	$100.50
Purchase #4	$76.75	13.592%	$87.1819	$87.18	$87.20	$87.20
Purchase #5	$135.88	6.330%	$144.4812	$144.48	$144.50	$144.50
Purchase #6	$26.87	12.273%	$30.1678	$30.17	$30.15	$30.20
Purchase #7	$108.86	3.868%	$113.0707	$113.07	$113.05	$113.10
7 purchase totals =	$671.13		$725.8751	$725.88	$725.90	$725.90