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	$83.43	7.249%	$89.4778	$89.48	$89.50	$89.50
Purchase #2	$54.45	4.272%	$56.7761	$56.78	$56.80	$56.80
Purchase #3	$237.47	11.873%	$265.6648	$265.66	$265.65	$265.70
Purchase #4	$234.63	4.189%	$244.4587	$244.46	$244.45	$244.50
Purchase #5	$188.32	11.574%	$210.1162	$210.12	$210.10	$210.10
Purchase #6	$149.49	12.760%	$168.5649	$168.56	$168.55	$168.60
Purchase #7	$140.39	13.161%	$158.8667	$158.87	$158.85	$158.90
7 purchase totals =	$1,088.18		$1,193.9252	$1,193.93	$1,193.90	$1,194.10