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	$200.80	13.684%	$228.2775	$228.28	$228.30	$228.30
Purchase #2	$222.53	11.577%	$248.2923	$248.29	$248.30	$248.30
Purchase #3	$48.59	8.256%	$52.6016	$52.60	$52.60	$52.60
Purchase #4	$99.89	10.543%	$110.4214	$110.42	$110.40	$110.40
Purchase #5	$33.92	9.711%	$37.214	$37.21	$37.20	$37.20
Purchase #6	$58.54	4.609%	$61.2381	$61.24	$61.25	$61.20
Purchase #7	$38.44	11.735%	$42.9509	$42.95	$42.95	$43.00
7 purchase totals =	$702.71		$780.9958	$780.99	$781.00	$781.00