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	$26.45	3.868%	$27.4731	$27.47	$27.45	$27.50
Purchase #2	$23.73	12.134%	$26.6094	$26.61	$26.60	$26.60
Purchase #3	$115.29	13.382%	$130.7181	$130.72	$130.70	$130.70
Purchase #4	$37.69	5.816%	$39.8821	$39.88	$39.90	$39.90
Purchase #5	$84.40	9.790%	$92.6628	$92.66	$92.65	$92.70
Purchase #6	$91.89	8.707%	$99.8909	$99.89	$99.90	$99.90
Purchase #7	$158.69	13.214%	$179.6593	$179.66	$179.65	$179.70
7 purchase totals =	$538.14		$596.8957	$596.89	$596.85	$597.00