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	$37.85	13.323%	$42.8928	$42.89	$42.90	$42.90
Purchase #2	$92.25	4.563%	$96.4594	$96.46	$96.45	$96.50
Purchase #3	$19.53	13.139%	$22.096	$22.10	$22.10	$22.10
Purchase #4	$181.48	8.442%	$196.8005	$196.80	$196.80	$196.80
Purchase #5	$68.98	4.776%	$72.2745	$72.27	$72.25	$72.30
Purchase #6	$156.92	7.115%	$168.0849	$168.08	$168.10	$168.10
Purchase #7	$69.80	13.863%	$79.4764	$79.48	$79.50	$79.50
7 purchase totals =	$626.81		$678.0845	$678.08	$678.10	$678.20