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	$27.29	6.660%	$29.1075	$29.11	$29.10	$29.10
Purchase #2	$216.70	7.607%	$233.1844	$233.18	$233.20	$233.20
Purchase #3	$126.67	8.467%	$137.3951	$137.40	$137.40	$137.40
Purchase #4	$31.53	12.293%	$35.406	$35.41	$35.40	$35.40
Purchase #5	$10.46	10.572%	$11.5658	$11.57	$11.55	$11.60
Purchase #6	$40.26	6.759%	$42.9812	$42.98	$43.00	$43.00
Purchase #7	$94.98	11.388%	$105.7963	$105.80	$105.80	$105.80
7 purchase totals =	$547.89		$595.4363	$595.45	$595.45	$595.50