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	$45.64	10.635%	$50.4938	$50.49	$50.50	$50.50
Purchase #2	$54.57	5.218%	$57.4175	$57.42	$57.40	$57.40
Purchase #3	$241.62	5.718%	$255.4358	$255.44	$255.45	$255.40
Purchase #4	$91.86	10.499%	$101.5044	$101.50	$101.50	$101.50
Purchase #5	$92.69	4.321%	$96.6951	$96.70	$96.70	$96.70
Purchase #6	$76.80	6.635%	$81.8957	$81.90	$81.90	$81.90
Purchase #7	$41.48	3.481%	$42.9239	$42.92	$42.90	$42.90
7 purchase totals =	$644.66		$686.3662	$686.37	$686.35	$686.30