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	$39.93	8.240%	$43.2202	$43.22	$43.20	$43.20
Purchase #2	$189.37	10.575%	$209.3959	$209.40	$209.40	$209.40
Purchase #3	$156.36	9.376%	$171.0203	$171.02	$171.00	$171.00
Purchase #4	$56.56	9.322%	$61.8325	$61.83	$61.85	$61.80
Purchase #5	$96.84	3.303%	$100.0386	$100.04	$100.05	$100.00
Purchase #6	$166.44	11.484%	$185.554	$185.55	$185.55	$185.60
Purchase #7	$67.27	10.776%	$74.519	$74.52	$74.50	$74.50
7 purchase totals =	$772.77		$845.5805	$845.58	$845.55	$845.50