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	$223.66	11.694%	$249.8148	$249.81	$249.80	$249.80
Purchase #2	$234.38	5.205%	$246.5795	$246.58	$246.60	$246.60
Purchase #3	$78.33	9.679%	$85.9116	$85.91	$85.90	$85.90
Purchase #4	$29.46	10.249%	$32.4794	$32.48	$32.50	$32.50
Purchase #5	$55.66	7.274%	$59.7087	$59.71	$59.70	$59.70
Purchase #6	$75.70	3.585%	$78.4138	$78.41	$78.40	$78.40
Purchase #7	$50.74	6.668%	$54.1233	$54.12	$54.10	$54.10
7 purchase totals =	$747.93		$807.0311	$807.02	$807.00	$807.00