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	$112.99	3.774%	$117.2542	$117.25	$117.25	$117.30
Purchase #2	$121.83	7.420%	$130.8698	$130.87	$130.85	$130.90
Purchase #3	$220.75	13.596%	$250.7632	$250.76	$250.75	$250.80
Purchase #4	$120.77	5.689%	$127.6406	$127.64	$127.65	$127.60
Purchase #5	$78.51	4.689%	$82.1913	$82.19	$82.20	$82.20
Purchase #6	$186.42	8.240%	$201.781	$201.78	$201.80	$201.80
Purchase #7	$60.55	11.284%	$67.3825	$67.38	$67.40	$67.40
7 purchase totals =	$901.82		$977.8826	$977.87	$977.90	$978.00