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	$111.97	13.717%	$127.3289	$127.33	$127.35	$127.30
Purchase #2	$55.35	7.610%	$59.5621	$59.56	$59.55	$59.60
Purchase #3	$109.94	8.200%	$118.9551	$118.96	$118.95	$119.00
Purchase #4	$32.89	3.204%	$33.9438	$33.94	$33.95	$33.90
Purchase #5	$140.73	12.366%	$158.1327	$158.13	$158.15	$158.10
Purchase #6	$136.87	3.109%	$141.1253	$141.13	$141.15	$141.10
Purchase #7	$191.70	7.271%	$205.6385	$205.64	$205.65	$205.60
7 purchase totals =	$779.45		$844.6864	$844.69	$844.75	$844.60