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	$45.83	11.453%	$51.0789	$51.08	$51.10	$51.10
Purchase #2	$78.69	13.575%	$89.3722	$89.37	$89.35	$89.40
Purchase #3	$113.81	13.460%	$129.1288	$129.13	$129.15	$129.10
Purchase #4	$162.54	5.798%	$171.9641	$171.96	$171.95	$172.00
Purchase #5	$179.57	11.683%	$200.5492	$200.55	$200.55	$200.50
Purchase #6	$9.48	13.558%	$10.7653	$10.77	$10.75	$10.80
Purchase #7	$83.77	7.361%	$89.9363	$89.94	$89.95	$89.90
7 purchase totals =	$673.69		$742.7948	$742.80	$742.80	$742.80