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	$88.54	11.850%	$99.032	$99.03	$99.05	$99.00
Purchase #2	$132.35	4.360%	$138.1205	$138.12	$138.10	$138.10
Purchase #3	$96.61	13.299%	$109.4582	$109.46	$109.45	$109.50
Purchase #4	$152.86	6.449%	$162.7179	$162.72	$162.70	$162.70
Purchase #5	$198.38	13.719%	$225.5958	$225.60	$225.60	$225.60
Purchase #6	$53.40	8.455%	$57.915	$57.92	$57.90	$57.90
Purchase #7	$53.92	13.169%	$61.0207	$61.02	$61.00	$61.00
7 purchase totals =	$776.06		$853.8601	$853.87	$853.80	$853.80