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	$30.84	4.531%	$32.2374	$32.24	$32.25	$32.20
Purchase #2	$238.87	6.712%	$254.903	$254.90	$254.90	$254.90
Purchase #3	$79.89	9.250%	$87.2798	$87.28	$87.30	$87.30
Purchase #4	$20.78	5.576%	$21.9387	$21.94	$21.95	$21.90
Purchase #5	$70.30	11.127%	$78.1223	$78.12	$78.10	$78.10
Purchase #6	$136.71	4.760%	$143.2174	$143.22	$143.20	$143.20
Purchase #7	$159.85	7.644%	$172.0689	$172.07	$172.05	$172.10
7 purchase totals =	$737.24		$789.7675	$789.77	$789.75	$789.70