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	$193.93	13.503%	$220.1164	$220.12	$220.10	$220.10
Purchase #2	$71.38	4.385%	$74.51	$74.51	$74.50	$74.50
Purchase #3	$84.69	7.373%	$90.9342	$90.93	$90.95	$90.90
Purchase #4	$174.33	9.258%	$190.4695	$190.47	$190.45	$190.50
Purchase #5	$138.59	3.277%	$143.1316	$143.13	$143.15	$143.10
Purchase #6	$242.70	12.844%	$273.8724	$273.87	$273.85	$273.90
Purchase #7	$23.84	4.310%	$24.8675	$24.87	$24.85	$24.90
7 purchase totals =	$929.46		$1,017.9016	$1,017.90	$1,017.85	$1,017.90