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	$36.91	7.741%	$39.7672	$39.77	$39.75	$39.80
Purchase #2	$193.66	3.174%	$199.8068	$199.81	$199.80	$199.80
Purchase #3	$85.39	13.829%	$97.1986	$97.20	$97.20	$97.20
Purchase #4	$94.91	4.829%	$99.4932	$99.49	$99.50	$99.50
Purchase #5	$196.85	12.638%	$221.7279	$221.73	$221.75	$221.70
Purchase #6	$207.61	3.814%	$215.5282	$215.53	$215.55	$215.50
Purchase #7	$112.80	13.271%	$127.7697	$127.77	$127.75	$127.80
7 purchase totals =	$928.13		$1,001.2916	$1,001.30	$1,001.30	$1,001.30