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	$86.91	13.279%	$98.4508	$98.45	$98.45	$98.50
Purchase #2	$104.52	8.282%	$113.1763	$113.18	$113.20	$113.20
Purchase #3	$177.96	7.225%	$190.8176	$190.82	$190.80	$190.80
Purchase #4	$249.89	11.368%	$278.2975	$278.30	$278.30	$278.30
Purchase #5	$10.34	11.355%	$11.5141	$11.51	$11.50	$11.50
Purchase #6	$10.84	5.118%	$11.3948	$11.39	$11.40	$11.40
Purchase #7	$66.27	6.382%	$70.4994	$70.50	$70.50	$70.50
7 purchase totals =	$706.73		$774.1505	$774.15	$774.15	$774.20