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	$85.88	5.442%	$90.5536	$90.55	$90.55	$90.60
Purchase #2	$23.68	3.821%	$24.5848	$24.58	$24.60	$24.60
Purchase #3	$79.74	9.444%	$87.2706	$87.27	$87.25	$87.30
Purchase #4	$32.56	9.175%	$35.5474	$35.55	$35.55	$35.50
Purchase #5	$137.49	13.289%	$155.761	$155.76	$155.75	$155.80
Purchase #6	$189.55	3.670%	$196.5065	$196.51	$196.50	$196.50
Purchase #7	$210.38	13.246%	$238.2469	$238.25	$238.25	$238.20
7 purchase totals =	$759.28		$828.4708	$828.47	$828.45	$828.50