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	$160.27	4.283%	$167.1344	$167.13	$167.15	$167.10
Purchase #2	$124.32	5.401%	$131.0345	$131.03	$131.05	$131.00
Purchase #3	$92.66	7.495%	$99.6049	$99.60	$99.60	$99.60
Purchase #4	$151.59	8.559%	$164.5646	$164.56	$164.55	$164.60
Purchase #5	$135.73	11.139%	$150.849	$150.85	$150.85	$150.80
Purchase #6	$46.83	11.238%	$52.0928	$52.09	$52.10	$52.10
Purchase #7	$86.78	10.443%	$95.8424	$95.84	$95.85	$95.80
7 purchase totals =	$798.18		$861.1226	$861.10	$861.15	$861.00