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	$83.61	12.814%	$94.3238	$94.32	$94.30	$94.30
Purchase #2	$184.52	3.378%	$190.7531	$190.75	$190.75	$190.80
Purchase #3	$16.39	9.223%	$17.9016	$17.90	$17.90	$17.90
Purchase #4	$147.88	12.502%	$166.368	$166.37	$166.35	$166.40
Purchase #5	$130.59	13.531%	$148.2601	$148.26	$148.25	$148.30
Purchase #6	$89.43	9.727%	$98.1289	$98.13	$98.15	$98.10
Purchase #7	$193.98	3.416%	$200.6064	$200.61	$200.60	$200.60
7 purchase totals =	$846.40		$916.3419	$916.34	$916.30	$916.40