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	$135.70	4.285%	$141.5147	$141.51	$141.50	$141.50
Purchase #2	$23.42	5.419%	$24.6891	$24.69	$24.70	$24.70
Purchase #3	$53.57	10.505%	$59.1975	$59.20	$59.20	$59.20
Purchase #4	$163.79	7.268%	$175.6943	$175.69	$175.70	$175.70
Purchase #5	$127.56	12.562%	$143.5841	$143.58	$143.60	$143.60
Purchase #6	$74.39	5.865%	$78.753	$78.75	$78.75	$78.80
Purchase #7	$28.89	9.418%	$31.6109	$31.61	$31.60	$31.60
7 purchase totals =	$607.32		$655.0436	$655.03	$655.05	$655.10