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	$17.34	10.511%	$19.1626	$19.16	$19.15	$19.20
Purchase #2	$81.64	10.473%	$90.1902	$90.19	$90.20	$90.20
Purchase #3	$203.42	13.217%	$230.306	$230.31	$230.30	$230.30
Purchase #4	$96.38	13.702%	$109.586	$109.59	$109.60	$109.60
Purchase #5	$250.50	11.768%	$279.9788	$279.98	$280.00	$280.00
Purchase #6	$21.80	3.740%	$22.6153	$22.62	$22.60	$22.60
Purchase #7	$37.70	8.795%	$41.0157	$41.02	$41.00	$41.00
7 purchase totals =	$708.78		$792.8546	$792.87	$792.85	$792.90