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	$100.25	8.717%	$108.9888	$108.99	$109.00	$109.00
Purchase #2	$200.47	13.342%	$227.2167	$227.22	$227.20	$227.20
Purchase #3	$10.66	10.817%	$11.8131	$11.81	$11.80	$11.80
Purchase #4	$82.53	9.331%	$90.2309	$90.23	$90.25	$90.20
Purchase #5	$100.74	10.436%	$111.2532	$111.25	$111.25	$111.30
Purchase #6	$29.70	10.740%	$32.8898	$32.89	$32.90	$32.90
Purchase #7	$153.84	6.601%	$163.995	$164.00	$164.00	$164.00
7 purchase totals =	$678.19		$746.3875	$746.39	$746.40	$746.40