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	$180.40	6.334%	$191.8265	$191.83	$191.85	$191.80
Purchase #2	$227.44	5.861%	$240.7703	$240.77	$240.75	$240.80
Purchase #3	$230.76	10.748%	$255.5621	$255.56	$255.55	$255.60
Purchase #4	$219.63	11.284%	$244.413	$244.41	$244.40	$244.40
Purchase #5	$80.26	11.731%	$89.6753	$89.68	$89.70	$89.70
Purchase #6	$59.79	4.694%	$62.5965	$62.60	$62.60	$62.60
Purchase #7	$204.59	11.609%	$228.3409	$228.34	$228.35	$228.30
7 purchase totals =	$1,202.87		$1,313.1846	$1,313.19	$1,313.20	$1,313.20