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	$128.37	12.381%	$144.2635	$144.26	$144.25	$144.30
Purchase #2	$216.55	8.154%	$234.2075	$234.21	$234.20	$234.20
Purchase #3	$244.77	11.350%	$272.5514	$272.55	$272.55	$272.60
Purchase #4	$142.69	9.435%	$156.1528	$156.15	$156.15	$156.20
Purchase #5	$29.48	13.870%	$33.5689	$33.57	$33.55	$33.60
Purchase #6	$169.39	9.224%	$185.0145	$185.01	$185.00	$185.00
Purchase #7	$29.35	12.128%	$32.9096	$32.91	$32.90	$32.90
7 purchase totals =	$960.60		$1,058.6682	$1,058.66	$1,058.60	$1,058.80