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	$85.75	4.498%	$89.607	$89.61	$89.60	$89.60
Purchase #2	$197.31	13.448%	$223.8442	$223.84	$223.85	$223.80
Purchase #3	$80.40	8.807%	$87.4808	$87.48	$87.50	$87.50
Purchase #4	$45.69	3.407%	$47.2467	$47.25	$47.25	$47.20
Purchase #5	$223.32	12.549%	$251.3444	$251.34	$251.35	$251.30
Purchase #6	$87.78	12.390%	$98.6559	$98.66	$98.65	$98.70
Purchase #7	$63.34	3.830%	$65.7659	$65.77	$65.75	$65.80
7 purchase totals =	$783.59		$863.9449	$863.95	$863.95	$863.90