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	$86.84	4.532%	$90.7756	$90.78	$90.80	$90.80
Purchase #2	$41.91	12.497%	$47.1475	$47.15	$47.15	$47.10
Purchase #3	$110.72	7.397%	$118.91	$118.91	$118.90	$118.90
Purchase #4	$148.30	8.421%	$160.7883	$160.79	$160.80	$160.80
Purchase #5	$77.39	6.772%	$82.6309	$82.63	$82.65	$82.60
Purchase #6	$160.34	11.784%	$179.2345	$179.23	$179.25	$179.20
Purchase #7	$75.47	8.366%	$81.7838	$81.78	$81.80	$81.80
7 purchase totals =	$700.97		$761.2706	$761.27	$761.35	$761.20