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	$27.86	7.505%	$29.9509	$29.95	$29.95	$30.00
Purchase #2	$186.72	6.381%	$198.6346	$198.63	$198.65	$198.60
Purchase #3	$113.82	9.716%	$124.8788	$124.88	$124.90	$124.90
Purchase #4	$178.81	6.818%	$191.0013	$191.00	$191.00	$191.00
Purchase #5	$180.93	8.632%	$196.5479	$196.55	$196.55	$196.50
Purchase #6	$67.43	4.667%	$70.577	$70.58	$70.60	$70.60
Purchase #7	$42.77	5.325%	$45.0475	$45.05	$45.05	$45.00
7 purchase totals =	$798.34		$856.6380	$856.64	$856.70	$856.60