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	$89.63	12.554%	$100.8822	$100.88	$100.90	$100.90
Purchase #2	$19.42	3.804%	$20.1587	$20.16	$20.15	$20.20
Purchase #3	$57.57	3.477%	$59.5717	$59.57	$59.55	$59.60
Purchase #4	$216.71	11.683%	$242.0282	$242.03	$242.05	$242.00
Purchase #5	$21.30	7.114%	$22.8153	$22.82	$22.80	$22.80
Purchase #6	$74.63	7.684%	$80.3646	$80.36	$80.35	$80.40
Purchase #7	$85.43	4.834%	$89.5597	$89.56	$89.55	$89.60
7 purchase totals =	$564.69		$615.3804	$615.38	$615.35	$615.50