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	$220.36	12.324%	$247.5172	$247.52	$247.50	$247.50
Purchase #2	$78.77	5.232%	$82.8912	$82.89	$82.90	$82.90
Purchase #3	$65.94	9.359%	$72.1113	$72.11	$72.10	$72.10
Purchase #4	$237.80	6.861%	$254.1155	$254.12	$254.10	$254.10
Purchase #5	$219.75	6.407%	$233.8294	$233.83	$233.85	$233.80
Purchase #6	$166.80	5.320%	$175.6738	$175.67	$175.65	$175.70
Purchase #7	$73.83	11.276%	$82.1551	$82.16	$82.15	$82.20
7 purchase totals =	$1,063.25		$1,148.2935	$1,148.30	$1,148.25	$1,148.30