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	$200.71	12.695%	$226.1901	$226.19	$226.20	$226.20
Purchase #2	$236.59	13.713%	$269.0336	$269.03	$269.05	$269.00
Purchase #3	$19.69	10.301%	$21.7183	$21.72	$21.70	$21.70
Purchase #4	$14.30	8.529%	$15.5196	$15.52	$15.50	$15.50
Purchase #5	$56.85	4.380%	$59.34	$59.34	$59.35	$59.30
Purchase #6	$93.76	10.240%	$103.361	$103.36	$103.35	$103.40
Purchase #7	$236.56	3.536%	$244.9248	$244.92	$244.90	$244.90
7 purchase totals =	$858.46		$940.0874	$940.08	$940.05	$940.00