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	$150.26	11.533%	$167.5895	$167.59	$167.60	$167.60
Purchase #2	$40.55	5.651%	$42.8415	$42.84	$42.85	$42.80
Purchase #3	$77.95	12.151%	$87.4217	$87.42	$87.40	$87.40
Purchase #4	$61.96	13.570%	$70.368	$70.37	$70.35	$70.40
Purchase #5	$194.74	7.413%	$209.1761	$209.18	$209.20	$209.20
Purchase #6	$72.99	8.115%	$78.9131	$78.91	$78.90	$78.90
Purchase #7	$172.40	11.269%	$191.8278	$191.83	$191.85	$191.80
7 purchase totals =	$770.85		$848.1377	$848.14	$848.15	$848.10