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	$42.30	6.682%	$45.1265	$45.13	$45.15	$45.10
Purchase #2	$98.76	10.146%	$108.7802	$108.78	$108.80	$108.80
Purchase #3	$22.40	6.361%	$23.8249	$23.82	$23.80	$23.80
Purchase #4	$243.62	11.655%	$272.0139	$272.01	$272.00	$272.00
Purchase #5	$85.32	8.146%	$92.2702	$92.27	$92.25	$92.30
Purchase #6	$117.25	12.429%	$131.823	$131.82	$131.80	$131.80
Purchase #7	$91.45	5.574%	$96.5474	$96.55	$96.55	$96.50
7 purchase totals =	$701.10		$770.3861	$770.38	$770.35	$770.30