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	$152.92	12.134%	$171.4753	$171.48	$171.50	$171.50
Purchase #2	$99.42	9.108%	$108.4752	$108.48	$108.50	$108.50
Purchase #3	$30.50	10.392%	$33.6696	$33.67	$33.65	$33.70
Purchase #4	$88.81	8.128%	$96.0285	$96.03	$96.05	$96.00
Purchase #5	$20.66	5.570%	$21.8108	$21.81	$21.80	$21.80
Purchase #6	$85.37	6.498%	$90.9173	$90.92	$90.90	$90.90
Purchase #7	$103.27	12.327%	$116.0001	$116.00	$116.00	$116.00
7 purchase totals =	$580.95		$638.3768	$638.39	$638.40	$638.40