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	$116.61	4.705%	$122.0965	$122.10	$122.10	$122.10
Purchase #2	$35.92	4.333%	$37.4764	$37.48	$37.50	$37.50
Purchase #3	$185.83	5.805%	$196.6174	$196.62	$196.60	$196.60
Purchase #4	$38.78	7.316%	$41.6171	$41.62	$41.60	$41.60
Purchase #5	$59.71	4.366%	$62.3169	$62.32	$62.30	$62.30
Purchase #6	$169.89	7.485%	$182.6063	$182.61	$182.60	$182.60
Purchase #7	$24.57	3.103%	$25.3324	$25.33	$25.35	$25.30
7 purchase totals =	$631.31		$668.0630	$668.08	$668.05	$668.00