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	$46.75	8.412%	$50.6826	$50.68	$50.70	$50.70
Purchase #2	$31.85	5.248%	$33.5215	$33.52	$33.50	$33.50
Purchase #3	$223.45	13.371%	$253.3275	$253.33	$253.35	$253.30
Purchase #4	$83.57	7.297%	$89.6681	$89.67	$89.65	$89.70
Purchase #5	$192.78	6.448%	$205.2105	$205.21	$205.20	$205.20
Purchase #6	$147.73	13.848%	$168.1877	$168.19	$168.20	$168.20
Purchase #7	$52.65	4.809%	$55.1819	$55.18	$55.20	$55.20
7 purchase totals =	$778.78		$855.7798	$855.78	$855.80	$855.80