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	$25.78	3.458%	$26.6715	$26.67	$26.65	$26.70
Purchase #2	$200.39	9.404%	$219.2347	$219.23	$219.25	$219.20
Purchase #3	$172.27	9.853%	$189.2438	$189.24	$189.25	$189.20
Purchase #4	$51.64	11.786%	$57.7263	$57.73	$57.75	$57.70
Purchase #5	$131.89	13.850%	$150.1568	$150.16	$150.15	$150.20
Purchase #6	$37.39	5.657%	$39.5052	$39.51	$39.50	$39.50
Purchase #7	$57.95	5.502%	$61.1384	$61.14	$61.15	$61.10
7 purchase totals =	$677.31		$743.6767	$743.68	$743.70	$743.60