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	$86.31	4.340%	$90.0559	$90.06	$90.05	$90.10
Purchase #2	$123.73	3.723%	$128.3365	$128.34	$128.35	$128.30
Purchase #3	$191.56	4.837%	$200.8258	$200.83	$200.85	$200.80
Purchase #4	$74.28	11.716%	$82.9826	$82.98	$83.00	$83.00
Purchase #5	$142.72	8.151%	$154.3531	$154.35	$154.35	$154.40
Purchase #6	$43.81	5.638%	$46.28	$46.28	$46.30	$46.30
Purchase #7	$127.35	10.867%	$141.1891	$141.19	$141.20	$141.20
7 purchase totals =	$789.76		$844.0230	$844.03	$844.10	$844.10