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	$60.81	5.618%	$64.2263	$64.23	$64.25	$64.20
Purchase #2	$200.47	11.200%	$222.9226	$222.92	$222.90	$222.90
Purchase #3	$143.64	5.265%	$151.2026	$151.20	$151.20	$151.20
Purchase #4	$134.73	8.332%	$145.9557	$145.96	$145.95	$146.00
Purchase #5	$124.65	10.172%	$137.3294	$137.33	$137.35	$137.30
Purchase #6	$240.96	6.383%	$256.3405	$256.34	$256.35	$256.30
Purchase #7	$106.61	10.779%	$118.1015	$118.10	$118.10	$118.10
7 purchase totals =	$1,011.87		$1,096.0786	$1,096.08	$1,096.10	$1,096.00