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	$177.87	5.421%	$187.5123	$187.51	$187.50	$187.50
Purchase #2	$30.29	10.525%	$33.478	$33.48	$33.50	$33.50
Purchase #3	$128.39	13.380%	$145.5686	$145.57	$145.55	$145.60
Purchase #4	$14.73	6.690%	$15.7154	$15.72	$15.70	$15.70
Purchase #5	$115.53	7.195%	$123.8424	$123.84	$123.85	$123.80
Purchase #6	$77.29	9.469%	$84.6086	$84.61	$84.60	$84.60
Purchase #7	$67.89	5.109%	$71.3585	$71.36	$71.35	$71.40
7 purchase totals =	$611.99		$662.0838	$662.09	$662.05	$662.10