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	$131.41	5.376%	$138.4746	$138.47	$138.45	$138.50
Purchase #2	$224.69	3.375%	$232.2733	$232.27	$232.25	$232.30
Purchase #3	$111.98	13.828%	$127.4646	$127.46	$127.45	$127.50
Purchase #4	$90.55	13.503%	$102.777	$102.78	$102.80	$102.80
Purchase #5	$84.64	6.524%	$90.1619	$90.16	$90.15	$90.20
Purchase #6	$58.69	3.593%	$60.7987	$60.80	$60.80	$60.80
Purchase #7	$31.48	11.175%	$34.9979	$35.00	$35.00	$35.00
7 purchase totals =	$733.44		$786.9480	$786.94	$786.90	$787.10