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	$41.91	7.339%	$44.9858	$44.99	$45.00	$45.00
Purchase #2	$237.27	13.108%	$268.3714	$268.37	$268.35	$268.40
Purchase #3	$166.95	10.764%	$184.9205	$184.92	$184.90	$184.90
Purchase #4	$180.84	4.680%	$189.3033	$189.30	$189.30	$189.30
Purchase #5	$28.82	12.503%	$32.4234	$32.42	$32.40	$32.40
Purchase #6	$81.89	9.319%	$89.5213	$89.52	$89.50	$89.50
Purchase #7	$130.35	9.278%	$142.4439	$142.44	$142.45	$142.40
7 purchase totals =	$868.03		$951.9696	$951.96	$951.90	$951.90