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	$25.38	3.270%	$26.2099	$26.21	$26.20	$26.20
Purchase #2	$250.57	7.845%	$270.2272	$270.23	$270.25	$270.20
Purchase #3	$87.30	3.798%	$90.6157	$90.62	$90.60	$90.60
Purchase #4	$83.85	13.687%	$95.3265	$95.33	$95.35	$95.30
Purchase #5	$66.98	11.808%	$74.889	$74.89	$74.90	$74.90
Purchase #6	$85.84	6.602%	$91.5072	$91.51	$91.50	$91.50
Purchase #7	$54.61	13.661%	$62.0703	$62.07	$62.05	$62.10
7 purchase totals =	$654.53		$710.8458	$710.86	$710.85	$710.80