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	$91.94	9.619%	$100.7837	$100.78	$100.80	$100.80
Purchase #2	$167.34	12.279%	$187.8877	$187.89	$187.90	$187.90
Purchase #3	$65.40	12.261%	$73.4187	$73.42	$73.40	$73.40
Purchase #4	$200.59	8.866%	$218.3743	$218.37	$218.35	$218.40
Purchase #5	$68.68	4.469%	$71.7493	$71.75	$71.75	$71.70
Purchase #6	$9.70	8.802%	$10.5538	$10.55	$10.55	$10.60
Purchase #7	$129.44	9.323%	$141.5077	$141.51	$141.50	$141.50
7 purchase totals =	$733.09		$804.2752	$804.27	$804.25	$804.30