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	$220.48	13.206%	$249.5966	$249.60	$249.60	$249.60
Purchase #2	$160.93	11.381%	$179.2454	$179.25	$179.25	$179.20
Purchase #3	$127.75	10.369%	$140.9964	$141.00	$141.00	$141.00
Purchase #4	$29.96	7.695%	$32.2654	$32.27	$32.25	$32.30
Purchase #5	$102.51	7.776%	$110.4812	$110.48	$110.50	$110.50
Purchase #6	$219.69	11.466%	$244.8797	$244.88	$244.90	$244.90
Purchase #7	$118.27	5.250%	$124.4792	$124.48	$124.50	$124.50
7 purchase totals =	$979.59		$1,081.9439	$1,081.96	$1,082.00	$1,082.00