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	$76.74	11.148%	$85.295	$85.30	$85.30	$85.30
Purchase #2	$184.47	6.785%	$196.9863	$196.99	$197.00	$197.00
Purchase #3	$203.94	9.530%	$223.3755	$223.38	$223.40	$223.40
Purchase #4	$134.95	3.290%	$139.3899	$139.39	$139.40	$139.40
Purchase #5	$12.68	3.334%	$13.1028	$13.10	$13.10	$13.10
Purchase #6	$37.76	12.553%	$42.5	$42.50	$42.50	$42.50
Purchase #7	$80.73	10.772%	$89.4262	$89.43	$89.45	$89.40
7 purchase totals =	$731.27		$790.0757	$790.09	$790.15	$790.10