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	$170.34	10.204%	$187.7215	$187.72	$187.70	$187.70
Purchase #2	$209.30	10.575%	$231.4335	$231.43	$231.45	$231.40
Purchase #3	$129.45	8.490%	$140.4403	$140.44	$140.45	$140.40
Purchase #4	$38.25	4.140%	$39.8336	$39.83	$39.85	$39.80
Purchase #5	$34.32	8.607%	$37.2739	$37.27	$37.25	$37.30
Purchase #6	$196.25	10.688%	$217.2252	$217.23	$217.25	$217.20
Purchase #7	$146.78	13.511%	$166.6114	$166.61	$166.60	$166.60
7 purchase totals =	$924.69		$1,020.5394	$1,020.53	$1,020.55	$1,020.40