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	$99.56	10.315%	$109.8296	$109.83	$109.85	$109.80
Purchase #2	$111.96	4.341%	$116.8202	$116.82	$116.80	$116.80
Purchase #3	$110.78	9.316%	$121.1003	$121.10	$121.10	$121.10
Purchase #4	$211.56	5.207%	$222.5759	$222.58	$222.60	$222.60
Purchase #5	$145.41	4.498%	$151.9505	$151.95	$151.95	$152.00
Purchase #6	$124.42	10.828%	$137.8922	$137.89	$137.90	$137.90
Purchase #7	$227.79	7.285%	$244.3845	$244.38	$244.40	$244.40
7 purchase totals =	$1,031.48		$1,104.5532	$1,104.55	$1,104.60	$1,104.60