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	$6.31	3.598%	$6.537	$6.54	$6.55	$6.50
Purchase #2	$75.91	12.160%	$85.1407	$85.14	$85.15	$85.10
Purchase #3	$165.94	13.766%	$188.7833	$188.78	$188.80	$188.80
Purchase #4	$181.39	10.362%	$200.1856	$200.19	$200.20	$200.20
Purchase #5	$219.82	3.536%	$227.5928	$227.59	$227.60	$227.60
Purchase #6	$190.41	3.641%	$197.3428	$197.34	$197.35	$197.30
Purchase #7	$11.89	13.735%	$13.5231	$13.52	$13.50	$13.50
7 purchase totals =	$851.67		$919.1053	$919.10	$919.15	$919.00