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	$15.56	11.276%	$17.3145	$17.31	$17.30	$17.30
Purchase #2	$39.32	3.107%	$40.5417	$40.54	$40.55	$40.50
Purchase #3	$46.28	8.164%	$50.0583	$50.06	$50.05	$50.10
Purchase #4	$229.91	4.441%	$240.1203	$240.12	$240.10	$240.10
Purchase #5	$72.78	8.566%	$79.0143	$79.01	$79.00	$79.00
Purchase #6	$128.25	7.435%	$137.7854	$137.79	$137.80	$137.80
Purchase #7	$45.76	13.325%	$51.8575	$51.86	$51.85	$51.90
7 purchase totals =	$577.86		$616.6920	$616.69	$616.65	$616.70