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	$103.29	13.513%	$117.2476	$117.25	$117.25	$117.20
Purchase #2	$48.91	6.345%	$52.0133	$52.01	$52.00	$52.00
Purchase #3	$199.26	13.377%	$225.915	$225.92	$225.90	$225.90
Purchase #4	$102.96	7.843%	$111.0352	$111.04	$111.05	$111.00
Purchase #5	$21.32	13.635%	$24.227	$24.23	$24.25	$24.20
Purchase #6	$114.80	13.369%	$130.1476	$130.15	$130.15	$130.10
Purchase #7	$114.98	8.520%	$124.7763	$124.78	$124.80	$124.80
7 purchase totals =	$705.52		$785.3620	$785.38	$785.40	$785.20