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	$114.90	4.683%	$120.2808	$120.28	$120.30	$120.30
Purchase #2	$36.29	4.501%	$37.9234	$37.92	$37.90	$37.90
Purchase #3	$137.57	9.223%	$150.2581	$150.26	$150.25	$150.30
Purchase #4	$59.29	5.171%	$62.3559	$62.36	$62.35	$62.40
Purchase #5	$226.47	7.668%	$243.8357	$243.84	$243.85	$243.80
Purchase #6	$45.98	11.262%	$51.1583	$51.16	$51.15	$51.20
Purchase #7	$84.54	6.554%	$90.0808	$90.08	$90.10	$90.10
7 purchase totals =	$705.04		$755.8930	$755.90	$755.90	$756.00