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	$83.77	6.802%	$89.468	$89.47	$89.45	$89.50
Purchase #2	$162.60	13.456%	$184.4795	$184.48	$184.50	$184.50
Purchase #3	$242.27	6.521%	$258.0684	$258.07	$258.05	$258.10
Purchase #4	$148.79	11.507%	$165.9113	$165.91	$165.90	$165.90
Purchase #5	$30.39	4.430%	$31.7363	$31.74	$31.75	$31.70
Purchase #6	$224.90	4.311%	$234.5954	$234.60	$234.60	$234.60
Purchase #7	$229.72	13.290%	$260.2498	$260.25	$260.25	$260.20
7 purchase totals =	$1,122.44		$1,224.5087	$1,224.52	$1,224.50	$1,224.50