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	$38.90	10.318%	$42.9137	$42.91	$42.90	$42.90
Purchase #2	$41.27	9.234%	$45.0809	$45.08	$45.10	$45.10
Purchase #3	$161.62	10.687%	$178.8923	$178.89	$178.90	$178.90
Purchase #4	$79.91	13.682%	$90.8433	$90.84	$90.85	$90.80
Purchase #5	$185.54	12.570%	$208.8624	$208.86	$208.85	$208.90
Purchase #6	$33.37	13.575%	$37.9	$37.90	$37.90	$37.90
Purchase #7	$203.89	3.729%	$211.4931	$211.49	$211.50	$211.50
7 purchase totals =	$744.50		$815.9857	$815.97	$816.00	$816.00