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	$56.56	6.111%	$60.0164	$60.02	$60.00	$60.00
Purchase #2	$39.89	8.611%	$43.3249	$43.32	$43.30	$43.30
Purchase #3	$214.45	13.735%	$243.9047	$243.90	$243.90	$243.90
Purchase #4	$10.64	6.696%	$11.3525	$11.35	$11.35	$11.40
Purchase #5	$16.68	10.782%	$18.4784	$18.48	$18.50	$18.50
Purchase #6	$43.45	4.151%	$45.2536	$45.25	$45.25	$45.30
Purchase #7	$239.79	12.843%	$270.5862	$270.59	$270.60	$270.60
7 purchase totals =	$621.46		$692.9167	$692.91	$692.90	$693.00