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	$67.78	7.540%	$72.8906	$72.89	$72.90	$72.90
Purchase #2	$235.93	13.348%	$267.4219	$267.42	$267.40	$267.40
Purchase #3	$140.78	12.168%	$157.9101	$157.91	$157.90	$157.90
Purchase #4	$130.46	9.662%	$143.065	$143.07	$143.05	$143.10
Purchase #5	$162.72	6.385%	$173.1097	$173.11	$173.10	$173.10
Purchase #6	$27.59	12.306%	$30.9852	$30.99	$31.00	$31.00
Purchase #7	$29.26	11.204%	$32.5383	$32.54	$32.55	$32.50
7 purchase totals =	$794.52		$877.9208	$877.93	$877.90	$877.90