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	$137.69	9.117%	$150.2432	$150.24	$150.25	$150.20
Purchase #2	$49.46	5.731%	$52.2946	$52.29	$52.30	$52.30
Purchase #3	$138.77	12.694%	$156.3855	$156.39	$156.40	$156.40
Purchase #4	$215.47	4.386%	$224.9205	$224.92	$224.90	$224.90
Purchase #5	$75.78	4.549%	$79.2272	$79.23	$79.25	$79.20
Purchase #6	$149.37	6.797%	$159.5227	$159.52	$159.50	$159.50
Purchase #7	$92.76	8.700%	$100.8301	$100.83	$100.85	$100.80
7 purchase totals =	$859.30		$923.4238	$923.42	$923.45	$923.30