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	$119.25	3.260%	$123.1376	$123.14	$123.15	$123.10
Purchase #2	$145.36	13.425%	$164.8746	$164.87	$164.85	$164.90
Purchase #3	$39.85	13.838%	$45.3644	$45.36	$45.35	$45.40
Purchase #4	$104.46	13.489%	$118.5506	$118.55	$118.55	$118.60
Purchase #5	$243.76	10.165%	$268.5382	$268.54	$268.55	$268.50
Purchase #6	$43.37	11.741%	$48.4621	$48.46	$48.45	$48.50
Purchase #7	$137.98	11.220%	$153.4614	$153.46	$153.45	$153.50
7 purchase totals =	$834.03		$922.3889	$922.38	$922.35	$922.50