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	$46.36	9.129%	$50.5922	$50.59	$50.60	$50.60
Purchase #2	$191.95	10.744%	$212.5731	$212.57	$212.55	$212.60
Purchase #3	$100.65	8.551%	$109.2566	$109.26	$109.25	$109.30
Purchase #4	$239.72	6.161%	$254.4891	$254.49	$254.50	$254.50
Purchase #5	$122.82	13.591%	$139.5125	$139.51	$139.50	$139.50
Purchase #6	$226.85	8.818%	$246.8536	$246.85	$246.85	$246.90
Purchase #7	$89.46	7.676%	$96.3269	$96.33	$96.35	$96.30
7 purchase totals =	$1,017.81		$1,109.6040	$1,109.60	$1,109.60	$1,109.70