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	$131.31	10.489%	$145.0831	$145.08	$145.10	$145.10
Purchase #2	$38.51	9.389%	$42.1257	$42.13	$42.15	$42.10
Purchase #3	$169.42	11.569%	$189.0202	$189.02	$189.00	$189.00
Purchase #4	$144.83	7.579%	$155.8067	$155.81	$155.80	$155.80
Purchase #5	$124.67	6.144%	$132.3297	$132.33	$132.35	$132.30
Purchase #6	$33.73	11.259%	$37.5277	$37.53	$37.55	$37.50
Purchase #7	$194.88	6.687%	$207.9116	$207.91	$207.90	$207.90
7 purchase totals =	$837.35		$909.8047	$909.81	$909.85	$909.70