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	$94.52	12.395%	$106.2358	$106.24	$106.25	$106.20
Purchase #2	$151.31	8.772%	$164.5829	$164.58	$164.60	$164.60
Purchase #3	$159.46	3.366%	$164.8274	$164.83	$164.85	$164.80
Purchase #4	$170.87	3.212%	$176.3583	$176.36	$176.35	$176.40
Purchase #5	$180.44	4.842%	$189.1769	$189.18	$189.20	$189.20
Purchase #6	$168.90	6.262%	$179.4765	$179.48	$179.50	$179.50
Purchase #7	$16.33	11.146%	$18.1501	$18.15	$18.15	$18.20
7 purchase totals =	$941.83		$998.8079	$998.82	$998.90	$998.90