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	$27.88	12.270%	$31.3009	$31.30	$31.30	$31.30
Purchase #2	$123.49	4.137%	$128.5988	$128.60	$128.60	$128.60
Purchase #3	$10.69	11.694%	$11.9401	$11.94	$11.95	$11.90
Purchase #4	$175.83	11.606%	$196.2368	$196.24	$196.25	$196.20
Purchase #5	$31.33	11.819%	$35.0329	$35.03	$35.05	$35.00
Purchase #6	$83.87	11.552%	$93.5587	$93.56	$93.55	$93.60
Purchase #7	$148.92	13.351%	$168.8023	$168.80	$168.80	$168.80
7 purchase totals =	$602.01		$665.4705	$665.47	$665.50	$665.40