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	$26.89	11.108%	$29.8769	$29.88	$29.90	$29.90
Purchase #2	$35.41	4.233%	$36.9089	$36.91	$36.90	$36.90
Purchase #3	$91.55	7.330%	$98.2606	$98.26	$98.25	$98.30
Purchase #4	$13.32	4.216%	$13.8816	$13.88	$13.90	$13.90
Purchase #5	$94.83	11.349%	$105.5923	$105.59	$105.60	$105.60
Purchase #6	$187.73	12.126%	$210.4941	$210.49	$210.50	$210.50
Purchase #7	$110.72	11.186%	$123.1051	$123.11	$123.10	$123.10
7 purchase totals =	$560.45		$618.1195	$618.12	$618.15	$618.20