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	$153.99	3.299%	$159.0701	$159.07	$159.05	$159.10
Purchase #2	$157.76	13.356%	$178.8304	$178.83	$178.85	$178.80
Purchase #3	$98.98	5.317%	$104.2428	$104.24	$104.25	$104.20
Purchase #4	$36.90	13.450%	$41.8631	$41.86	$41.85	$41.90
Purchase #5	$29.91	12.230%	$33.568	$33.57	$33.55	$33.60
Purchase #6	$100.37	4.665%	$105.0523	$105.05	$105.05	$105.10
Purchase #7	$76.89	11.312%	$85.5878	$85.59	$85.60	$85.60
7 purchase totals =	$654.80		$708.2145	$708.21	$708.20	$708.30