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	$138.50	12.181%	$155.3707	$155.37	$155.35	$155.40
Purchase #2	$53.28	8.805%	$57.9713	$57.97	$57.95	$58.00
Purchase #3	$229.43	11.306%	$255.3694	$255.37	$255.35	$255.40
Purchase #4	$102.92	6.577%	$109.689	$109.69	$109.70	$109.70
Purchase #5	$51.51	13.388%	$58.4062	$58.41	$58.40	$58.40
Purchase #6	$30.49	11.389%	$33.9625	$33.96	$33.95	$34.00
Purchase #7	$185.85	5.498%	$196.068	$196.07	$196.05	$196.10
7 purchase totals =	$791.98		$866.8371	$866.84	$866.75	$867.00