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	$11.89	3.315%	$12.2842	$12.28	$12.30	$12.30
Purchase #2	$40.79	3.470%	$42.2054	$42.21	$42.20	$42.20
Purchase #3	$85.28	5.758%	$90.1904	$90.19	$90.20	$90.20
Purchase #4	$226.40	12.168%	$253.9484	$253.95	$253.95	$253.90
Purchase #5	$178.31	11.700%	$199.1723	$199.17	$199.15	$199.20
Purchase #6	$138.68	11.688%	$154.8889	$154.89	$154.90	$154.90
Purchase #7	$34.41	9.383%	$37.6387	$37.64	$37.65	$37.60
7 purchase totals =	$715.76		$790.3283	$790.33	$790.35	$790.30