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	$53.41	12.197%	$59.9244	$59.92	$59.90	$59.90
Purchase #2	$163.68	9.199%	$178.7369	$178.74	$178.75	$178.70
Purchase #3	$140.70	8.645%	$152.8635	$152.86	$152.85	$152.90
Purchase #4	$56.52	11.547%	$63.0464	$63.05	$63.05	$63.00
Purchase #5	$187.73	5.171%	$197.4375	$197.44	$197.45	$197.40
Purchase #6	$137.57	13.712%	$156.4336	$156.43	$156.45	$156.40
Purchase #7	$106.93	4.185%	$111.405	$111.41	$111.40	$111.40
7 purchase totals =	$846.54		$919.8473	$919.85	$919.85	$919.70