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	$137.56	13.859%	$156.6244	$156.62	$156.60	$156.60
Purchase #2	$76.39	8.329%	$82.7525	$82.75	$82.75	$82.80
Purchase #3	$167.62	13.873%	$190.8739	$190.87	$190.85	$190.90
Purchase #4	$89.76	9.287%	$98.096	$98.10	$98.10	$98.10
Purchase #5	$17.56	7.122%	$18.8106	$18.81	$18.80	$18.80
Purchase #6	$60.78	5.496%	$64.1205	$64.12	$64.10	$64.10
Purchase #7	$64.44	8.364%	$69.8298	$69.83	$69.85	$69.80
7 purchase totals =	$614.11		$681.1077	$681.10	$681.05	$681.10