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	$28.63	8.718%	$31.126	$31.13	$31.15	$31.10
Purchase #2	$30.86	6.777%	$32.9514	$32.95	$32.95	$33.00
Purchase #3	$177.68	12.804%	$200.4301	$200.43	$200.45	$200.40
Purchase #4	$157.71	8.569%	$171.2242	$171.22	$171.20	$171.20
Purchase #5	$32.65	9.612%	$35.7883	$35.79	$35.80	$35.80
Purchase #6	$44.45	12.336%	$49.9334	$49.93	$49.95	$49.90
Purchase #7	$137.36	6.155%	$145.8145	$145.81	$145.80	$145.80
7 purchase totals =	$609.34		$667.2679	$667.26	$667.30	$667.20