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	$100.88	7.265%	$108.2089	$108.21	$108.20	$108.20
Purchase #2	$29.89	6.555%	$31.8493	$31.85	$31.85	$31.80
Purchase #3	$116.91	7.421%	$125.5859	$125.59	$125.60	$125.60
Purchase #4	$85.30	6.162%	$90.5562	$90.56	$90.55	$90.60
Purchase #5	$24.68	13.540%	$28.0217	$28.02	$28.00	$28.00
Purchase #6	$89.66	6.115%	$95.1427	$95.14	$95.15	$95.10
Purchase #7	$73.60	4.410%	$76.8458	$76.85	$76.85	$76.80
7 purchase totals =	$520.92		$556.2105	$556.22	$556.20	$556.10