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	$28.61	12.420%	$32.1634	$32.16	$32.15	$32.20
Purchase #2	$175.33	7.223%	$187.9941	$187.99	$188.00	$188.00
Purchase #3	$173.72	8.712%	$188.8545	$188.85	$188.85	$188.90
Purchase #4	$195.31	13.528%	$221.7315	$221.73	$221.75	$221.70
Purchase #5	$18.27	5.256%	$19.2303	$19.23	$19.25	$19.20
Purchase #6	$149.80	12.380%	$168.3452	$168.35	$168.35	$168.30
Purchase #7	$52.59	12.464%	$59.1448	$59.14	$59.15	$59.10
7 purchase totals =	$793.63		$877.4638	$877.45	$877.50	$877.40