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	$37.36	11.267%	$41.5694	$41.57	$41.55	$41.60
Purchase #2	$181.76	4.574%	$190.0737	$190.07	$190.05	$190.10
Purchase #3	$96.65	3.524%	$100.0559	$100.06	$100.05	$100.10
Purchase #4	$180.49	13.699%	$205.2153	$205.22	$205.20	$205.20
Purchase #5	$50.29	4.175%	$52.3896	$52.39	$52.40	$52.40
Purchase #6	$39.64	9.267%	$43.3134	$43.31	$43.30	$43.30
Purchase #7	$35.54	5.354%	$37.4428	$37.44	$37.45	$37.40
7 purchase totals =	$621.73		$670.0601	$670.06	$670.00	$670.10