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	$67.58	5.474%	$71.2793	$71.28	$71.30	$71.30
Purchase #2	$33.27	12.761%	$37.5156	$37.52	$37.50	$37.50
Purchase #3	$221.90	11.578%	$247.5916	$247.59	$247.60	$247.60
Purchase #4	$131.90	12.378%	$148.2266	$148.23	$148.25	$148.20
Purchase #5	$81.99	7.256%	$87.9392	$87.94	$87.95	$87.90
Purchase #6	$134.72	11.848%	$150.6816	$150.68	$150.70	$150.70
Purchase #7	$91.88	7.126%	$98.4274	$98.43	$98.45	$98.40
7 purchase totals =	$763.24		$841.6613	$841.67	$841.75	$841.60