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	$106.83	4.168%	$111.2827	$111.28	$111.30	$111.30
Purchase #2	$80.99	12.175%	$90.8505	$90.85	$90.85	$90.90
Purchase #3	$227.36	13.542%	$258.1491	$258.15	$258.15	$258.10
Purchase #4	$218.83	11.442%	$243.8685	$243.87	$243.85	$243.90
Purchase #5	$12.55	4.502%	$13.115	$13.12	$13.10	$13.10
Purchase #6	$54.52	4.447%	$56.9445	$56.94	$56.95	$56.90
Purchase #7	$149.59	6.771%	$159.7187	$159.72	$159.70	$159.70
7 purchase totals =	$850.67		$933.9290	$933.93	$933.90	$933.90