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	$76.33	9.767%	$83.7852	$83.79	$83.80	$83.80
Purchase #2	$111.87	5.245%	$117.7376	$117.74	$117.75	$117.70
Purchase #3	$125.49	11.510%	$139.9339	$139.93	$139.95	$139.90
Purchase #4	$154.68	4.864%	$162.2036	$162.20	$162.20	$162.20
Purchase #5	$91.72	8.259%	$99.2952	$99.30	$99.30	$99.30
Purchase #6	$39.86	8.623%	$43.2971	$43.30	$43.30	$43.30
Purchase #7	$136.90	10.220%	$150.8912	$150.89	$150.90	$150.90
7 purchase totals =	$736.85		$797.1438	$797.15	$797.20	$797.10