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	$247.57	11.373%	$275.7261	$275.73	$275.75	$275.70
Purchase #2	$232.79	12.758%	$262.4893	$262.49	$262.50	$262.50
Purchase #3	$96.92	13.814%	$110.3085	$110.31	$110.30	$110.30
Purchase #4	$90.67	6.165%	$96.2598	$96.26	$96.25	$96.30
Purchase #5	$49.36	8.478%	$53.5447	$53.54	$53.55	$53.50
Purchase #6	$213.36	4.362%	$222.6668	$222.67	$222.65	$222.70
Purchase #7	$151.89	5.123%	$159.6713	$159.67	$159.65	$159.70
7 purchase totals =	$1,082.56		$1,180.6665	$1,180.67	$1,180.65	$1,180.70