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	$214.97	13.695%	$244.4101	$244.41	$244.40	$244.40
Purchase #2	$107.74	13.675%	$122.4734	$122.47	$122.45	$122.50
Purchase #3	$71.99	13.449%	$81.6719	$81.67	$81.65	$81.70
Purchase #4	$213.99	4.435%	$223.4805	$223.48	$223.50	$223.50
Purchase #5	$81.57	9.152%	$89.0353	$89.04	$89.05	$89.00
Purchase #6	$80.73	10.781%	$89.4335	$89.43	$89.45	$89.40
Purchase #7	$40.48	6.118%	$42.9566	$42.96	$42.95	$43.00
7 purchase totals =	$811.47		$893.4613	$893.46	$893.45	$893.50