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	$144.91	13.296%	$164.1772	$164.18	$164.20	$164.20
Purchase #2	$80.69	6.107%	$85.6177	$85.62	$85.60	$85.60
Purchase #3	$57.37	10.608%	$63.4558	$63.46	$63.45	$63.50
Purchase #4	$112.46	7.168%	$120.5211	$120.52	$120.50	$120.50
Purchase #5	$227.30	10.188%	$250.4573	$250.46	$250.45	$250.50
Purchase #6	$14.69	4.310%	$15.3231	$15.32	$15.30	$15.30
Purchase #7	$67.96	11.151%	$75.5382	$75.54	$75.55	$75.50
7 purchase totals =	$705.38		$775.0904	$775.10	$775.05	$775.10