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	$109.86	9.867%	$120.6999	$120.70	$120.70	$120.70
Purchase #2	$18.91	8.316%	$20.4826	$20.48	$20.50	$20.50
Purchase #3	$241.59	4.539%	$252.5558	$252.56	$252.55	$252.60
Purchase #4	$104.55	7.355%	$112.2397	$112.24	$112.25	$112.20
Purchase #5	$222.63	7.287%	$238.853	$238.85	$238.85	$238.90
Purchase #6	$195.95	11.160%	$217.818	$217.82	$217.80	$217.80
Purchase #7	$82.60	6.746%	$88.1722	$88.17	$88.15	$88.20
7 purchase totals =	$976.09		$1,050.8212	$1,050.82	$1,050.80	$1,050.90