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	$116.81	3.467%	$120.8598	$120.86	$120.85	$120.90
Purchase #2	$220.38	5.704%	$232.9505	$232.95	$232.95	$233.00
Purchase #3	$135.46	9.559%	$148.4086	$148.41	$148.40	$148.40
Purchase #4	$44.67	12.487%	$50.2479	$50.25	$50.25	$50.20
Purchase #5	$36.50	3.812%	$37.8914	$37.89	$37.90	$37.90
Purchase #6	$39.64	8.812%	$43.1331	$43.13	$43.15	$43.10
Purchase #7	$162.95	13.784%	$185.411	$185.41	$185.40	$185.40
7 purchase totals =	$756.41		$818.9023	$818.90	$818.90	$818.90