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	$80.80	11.637%	$90.2027	$90.20	$90.20	$90.20
Purchase #2	$143.69	11.762%	$160.5908	$160.59	$160.60	$160.60
Purchase #3	$100.44	10.378%	$110.8637	$110.86	$110.85	$110.90
Purchase #4	$83.97	8.399%	$91.0226	$91.02	$91.00	$91.00
Purchase #5	$78.47	5.153%	$82.5136	$82.51	$82.50	$82.50
Purchase #6	$117.66	7.802%	$126.8398	$126.84	$126.85	$126.80
Purchase #7	$235.90	4.476%	$246.4589	$246.46	$246.45	$246.50
7 purchase totals =	$840.93		$908.4921	$908.48	$908.45	$908.50