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	$173.28	10.170%	$190.9026	$190.90	$190.90	$190.90
Purchase #2	$212.35	5.874%	$224.8234	$224.82	$224.80	$224.80
Purchase #3	$36.39	12.460%	$40.9242	$40.92	$40.90	$40.90
Purchase #4	$243.53	13.807%	$277.1542	$277.15	$277.15	$277.20
Purchase #5	$38.77	11.824%	$43.3542	$43.35	$43.35	$43.40
Purchase #6	$155.53	7.271%	$166.8386	$166.84	$166.85	$166.80
Purchase #7	$24.52	13.669%	$27.8716	$27.87	$27.85	$27.90
7 purchase totals =	$884.37		$971.8688	$971.85	$971.80	$971.90