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	$31.97	6.126%	$33.9285	$33.93	$33.95	$33.90
Purchase #2	$41.94	3.505%	$43.41	$43.41	$43.40	$43.40
Purchase #3	$152.25	5.773%	$161.0394	$161.04	$161.05	$161.00
Purchase #4	$46.37	8.226%	$50.1844	$50.18	$50.20	$50.20
Purchase #5	$123.78	11.417%	$137.912	$137.91	$137.90	$137.90
Purchase #6	$82.26	11.438%	$91.6689	$91.67	$91.65	$91.70
Purchase #7	$73.31	9.301%	$80.1286	$80.13	$80.15	$80.10
7 purchase totals =	$551.88		$598.2718	$598.27	$598.30	$598.20