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	$30.94	6.632%	$32.9919	$32.99	$33.00	$33.00
Purchase #2	$149.85	11.651%	$167.309	$167.31	$167.30	$167.30
Purchase #3	$134.75	8.770%	$146.5676	$146.57	$146.55	$146.60
Purchase #4	$88.83	4.233%	$92.5902	$92.59	$92.60	$92.60
Purchase #5	$239.57	13.259%	$271.3346	$271.33	$271.35	$271.30
Purchase #6	$88.73	12.288%	$99.6331	$99.63	$99.65	$99.60
Purchase #7	$45.82	9.616%	$50.2261	$50.23	$50.25	$50.20
7 purchase totals =	$778.49		$860.6525	$860.65	$860.70	$860.60