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	$163.90	12.503%	$184.3924	$184.39	$184.40	$184.40
Purchase #2	$242.52	7.810%	$261.4608	$261.46	$261.45	$261.50
Purchase #3	$160.27	13.217%	$181.4529	$181.45	$181.45	$181.50
Purchase #4	$231.54	8.701%	$251.6863	$251.69	$251.70	$251.70
Purchase #5	$169.49	12.281%	$190.3051	$190.31	$190.30	$190.30
Purchase #6	$18.62	8.678%	$20.2358	$20.24	$20.25	$20.20
Purchase #7	$34.38	8.615%	$37.3418	$37.34	$37.35	$37.30
7 purchase totals =	$1,020.72		$1,126.8751	$1,126.88	$1,126.90	$1,126.90