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	$132.55	7.585%	$142.6039	$142.60	$142.60	$142.60
Purchase #2	$171.65	10.261%	$189.263	$189.26	$189.25	$189.30
Purchase #3	$23.74	8.112%	$25.6658	$25.67	$25.65	$25.70
Purchase #4	$35.50	5.503%	$37.4536	$37.45	$37.45	$37.50
Purchase #5	$189.39	11.146%	$210.4994	$210.50	$210.50	$210.50
Purchase #6	$145.56	7.791%	$156.9006	$156.90	$156.90	$156.90
Purchase #7	$128.29	10.129%	$141.2845	$141.28	$141.30	$141.30
7 purchase totals =	$826.68		$903.6708	$903.66	$903.65	$903.80