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	$38.37	10.120%	$42.253	$42.25	$42.25	$42.30
Purchase #2	$179.85	10.580%	$198.8781	$198.88	$198.90	$198.90
Purchase #3	$167.38	13.529%	$190.0248	$190.02	$190.00	$190.00
Purchase #4	$219.56	13.580%	$249.3762	$249.38	$249.40	$249.40
Purchase #5	$123.62	9.478%	$135.3367	$135.34	$135.35	$135.30
Purchase #6	$231.54	10.291%	$255.3678	$255.37	$255.35	$255.40
Purchase #7	$208.25	12.476%	$234.2313	$234.23	$234.25	$234.20
7 purchase totals =	$1,168.57		$1,305.4679	$1,305.47	$1,305.50	$1,305.50