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	$236.46	8.191%	$255.8284	$255.83	$255.85	$255.80
Purchase #2	$6.38	3.349%	$6.5937	$6.59	$6.60	$6.60
Purchase #3	$217.52	6.155%	$230.9084	$230.91	$230.90	$230.90
Purchase #4	$82.96	7.640%	$89.2981	$89.30	$89.30	$89.30
Purchase #5	$22.54	13.319%	$25.5421	$25.54	$25.55	$25.50
Purchase #6	$191.65	9.172%	$209.2281	$209.23	$209.25	$209.20
Purchase #7	$95.69	8.680%	$103.9959	$104.00	$104.00	$104.00
7 purchase totals =	$853.20		$921.3947	$921.40	$921.45	$921.30