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	$20.88	11.807%	$23.3453	$23.35	$23.35	$23.30
Purchase #2	$59.50	11.193%	$66.1598	$66.16	$66.15	$66.20
Purchase #3	$91.50	9.192%	$99.9107	$99.91	$99.90	$99.90
Purchase #4	$90.98	6.174%	$96.5971	$96.60	$96.60	$96.60
Purchase #5	$20.35	3.530%	$21.0684	$21.07	$21.05	$21.10
Purchase #6	$187.92	4.361%	$196.1152	$196.12	$196.10	$196.10
Purchase #7	$31.49	13.725%	$35.812	$35.81	$35.80	$35.80
7 purchase totals =	$502.62		$539.0085	$539.02	$538.95	$539.00