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	$98.31	11.106%	$109.2283	$109.23	$109.25	$109.20
Purchase #2	$140.47	4.232%	$146.4147	$146.41	$146.40	$146.40
Purchase #3	$128.81	9.836%	$141.4798	$141.48	$141.50	$141.50
Purchase #4	$68.91	11.324%	$76.7134	$76.71	$76.70	$76.70
Purchase #5	$52.88	8.789%	$57.5276	$57.53	$57.55	$57.50
Purchase #6	$175.71	13.366%	$199.1954	$199.20	$199.20	$199.20
Purchase #7	$93.31	11.627%	$104.1592	$104.16	$104.15	$104.20
7 purchase totals =	$758.40		$834.7184	$834.72	$834.75	$834.70