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	$17.97	13.171%	$20.3368	$20.34	$20.35	$20.30
Purchase #2	$27.50	3.546%	$28.4752	$28.48	$28.50	$28.50
Purchase #3	$83.42	12.437%	$93.7949	$93.79	$93.80	$93.80
Purchase #4	$9.37	12.789%	$10.5683	$10.57	$10.55	$10.60
Purchase #5	$205.80	8.483%	$223.258	$223.26	$223.25	$223.30
Purchase #6	$109.91	4.310%	$114.6471	$114.65	$114.65	$114.60
Purchase #7	$36.51	13.295%	$41.364	$41.36	$41.35	$41.40
7 purchase totals =	$490.48		$532.4443	$532.45	$532.45	$532.50