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	$93.99	6.627%	$100.2187	$100.22	$100.20	$100.20
Purchase #2	$89.50	10.767%	$99.1365	$99.14	$99.15	$99.10
Purchase #3	$188.28	5.783%	$199.1682	$199.17	$199.15	$199.20
Purchase #4	$96.36	10.425%	$106.4055	$106.41	$106.40	$106.40
Purchase #5	$137.73	6.669%	$146.9152	$146.92	$146.90	$146.90
Purchase #6	$39.86	7.828%	$42.9802	$42.98	$43.00	$43.00
Purchase #7	$98.57	5.596%	$104.086	$104.09	$104.10	$104.10
7 purchase totals =	$744.29		$798.9103	$798.93	$798.90	$798.90