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	$33.40	6.742%	$35.6518	$35.65	$35.65	$35.70
Purchase #2	$42.75	4.295%	$44.5861	$44.59	$44.60	$44.60
Purchase #3	$237.95	4.383%	$248.3793	$248.38	$248.40	$248.40
Purchase #4	$122.92	3.695%	$127.4619	$127.46	$127.45	$127.50
Purchase #5	$21.90	3.146%	$22.589	$22.59	$22.60	$22.60
Purchase #6	$51.46	6.106%	$54.6021	$54.60	$54.60	$54.60
Purchase #7	$7.83	9.306%	$8.5587	$8.56	$8.55	$8.60
7 purchase totals =	$518.21		$541.8289	$541.83	$541.85	$542.00