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	$42.26	3.139%	$43.5865	$43.59	$43.60	$43.60
Purchase #2	$87.27	9.414%	$95.4856	$95.49	$95.50	$95.50
Purchase #3	$228.30	3.834%	$237.053	$237.05	$237.05	$237.10
Purchase #4	$174.41	4.549%	$182.3439	$182.34	$182.35	$182.30
Purchase #5	$21.28	5.645%	$22.4813	$22.48	$22.50	$22.50
Purchase #6	$44.34	3.353%	$45.8267	$45.83	$45.85	$45.80
Purchase #7	$32.67	3.401%	$33.7811	$33.78	$33.80	$33.80
7 purchase totals =	$630.53		$660.5581	$660.56	$660.65	$660.60