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	$89.91	10.746%	$99.5717	$99.57	$99.55	$99.60
Purchase #2	$84.86	4.346%	$88.548	$88.55	$88.55	$88.50
Purchase #3	$172.50	5.680%	$182.298	$182.30	$182.30	$182.30
Purchase #4	$29.68	13.326%	$33.6352	$33.64	$33.65	$33.60
Purchase #5	$82.88	10.507%	$91.5882	$91.59	$91.60	$91.60
Purchase #6	$30.69	11.757%	$34.2982	$34.30	$34.30	$34.30
Purchase #7	$170.94	12.221%	$191.8306	$191.83	$191.85	$191.80
7 purchase totals =	$661.46		$721.7699	$721.78	$721.80	$721.70