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	$14.50	9.129%	$15.8237	$15.82	$15.80	$15.80
Purchase #2	$156.75	7.294%	$168.1833	$168.18	$168.20	$168.20
Purchase #3	$103.92	8.364%	$112.6119	$112.61	$112.60	$112.60
Purchase #4	$110.64	13.636%	$125.7269	$125.73	$125.75	$125.70
Purchase #5	$197.69	12.595%	$222.5891	$222.59	$222.60	$222.60
Purchase #6	$158.55	8.164%	$171.494	$171.49	$171.50	$171.50
Purchase #7	$138.27	12.188%	$155.1223	$155.12	$155.10	$155.10
7 purchase totals =	$880.32		$971.5512	$971.54	$971.55	$971.50