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	$146.32	13.759%	$166.4522	$166.45	$166.45	$166.50
Purchase #2	$180.82	8.610%	$196.3886	$196.39	$196.40	$196.40
Purchase #3	$63.89	3.492%	$66.121	$66.12	$66.10	$66.10
Purchase #4	$157.42	11.141%	$174.9582	$174.96	$174.95	$175.00
Purchase #5	$106.72	10.469%	$117.8925	$117.89	$117.90	$117.90
Purchase #6	$123.77	4.601%	$129.4647	$129.46	$129.45	$129.50
Purchase #7	$201.72	13.584%	$229.1216	$229.12	$229.10	$229.10
7 purchase totals =	$980.66		$1,080.3988	$1,080.39	$1,080.35	$1,080.50