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	$82.79	3.221%	$85.4567	$85.46	$85.45	$85.50
Purchase #2	$116.41	6.314%	$123.7601	$123.76	$123.75	$123.80
Purchase #3	$238.35	13.727%	$271.0683	$271.07	$271.05	$271.10
Purchase #4	$149.90	4.666%	$156.8943	$156.89	$156.90	$156.90
Purchase #5	$16.90	5.574%	$17.842	$17.84	$17.85	$17.80
Purchase #6	$149.93	6.310%	$159.3906	$159.39	$159.40	$159.40
Purchase #7	$40.52	8.672%	$44.0339	$44.03	$44.05	$44.00
7 purchase totals =	$794.80		$858.4459	$858.44	$858.45	$858.50