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	$31.55	8.658%	$34.2816	$34.28	$34.30	$34.30
Purchase #2	$136.54	10.223%	$150.4985	$150.50	$150.50	$150.50
Purchase #3	$55.91	6.148%	$59.3473	$59.35	$59.35	$59.30
Purchase #4	$12.25	12.391%	$13.7679	$13.77	$13.75	$13.80
Purchase #5	$248.67	6.757%	$265.4726	$265.47	$265.45	$265.50
Purchase #6	$42.76	6.602%	$45.583	$45.58	$45.60	$45.60
Purchase #7	$232.76	7.530%	$250.2868	$250.29	$250.30	$250.30
7 purchase totals =	$760.44		$819.2377	$819.24	$819.25	$819.30