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	$26.34	3.400%	$27.2356	$27.24	$27.25	$27.20
Purchase #2	$41.26	11.358%	$45.9463	$45.95	$45.95	$45.90
Purchase #3	$80.95	13.742%	$92.0741	$92.07	$92.05	$92.10
Purchase #4	$59.39	5.354%	$62.5697	$62.57	$62.55	$62.60
Purchase #5	$78.42	13.777%	$89.2239	$89.22	$89.20	$89.20
Purchase #6	$72.29	5.400%	$76.1937	$76.19	$76.20	$76.20
Purchase #7	$182.63	7.222%	$195.8195	$195.82	$195.80	$195.80
7 purchase totals =	$541.28		$589.0628	$589.06	$589.00	$589.00