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	$123.42	5.174%	$129.8058	$129.81	$129.80	$129.80
Purchase #2	$164.89	12.521%	$185.5359	$185.54	$185.55	$185.50
Purchase #3	$59.83	12.840%	$67.5122	$67.51	$67.50	$67.50
Purchase #4	$38.40	3.521%	$39.7521	$39.75	$39.75	$39.80
Purchase #5	$64.78	10.661%	$71.6862	$71.69	$71.70	$71.70
Purchase #6	$60.49	13.788%	$68.8304	$68.83	$68.85	$68.80
Purchase #7	$137.34	9.476%	$150.3543	$150.35	$150.35	$150.40
7 purchase totals =	$649.15		$713.4769	$713.48	$713.50	$713.50