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	$131.92	11.649%	$147.2874	$147.29	$147.30	$147.30
Purchase #2	$120.26	6.308%	$127.846	$127.85	$127.85	$127.80
Purchase #3	$93.38	10.321%	$103.0177	$103.02	$103.00	$103.00
Purchase #4	$151.69	5.760%	$160.4273	$160.43	$160.45	$160.40
Purchase #5	$175.61	9.774%	$192.7741	$192.77	$192.75	$192.80
Purchase #6	$90.61	12.385%	$101.832	$101.83	$101.85	$101.80
Purchase #7	$35.96	10.210%	$39.6315	$39.63	$39.65	$39.60
7 purchase totals =	$799.43		$872.8160	$872.82	$872.85	$872.70