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	$75.69	10.710%	$83.7964	$83.80	$83.80	$83.80
Purchase #2	$234.66	5.511%	$247.5921	$247.59	$247.60	$247.60
Purchase #3	$87.99	5.200%	$92.5655	$92.57	$92.55	$92.60
Purchase #4	$11.91	13.651%	$13.5358	$13.54	$13.55	$13.50
Purchase #5	$17.82	9.418%	$19.4983	$19.50	$19.50	$19.50
Purchase #6	$39.31	6.593%	$41.9017	$41.90	$41.90	$41.90
Purchase #7	$156.92	7.576%	$168.8083	$168.81	$168.80	$168.80
7 purchase totals =	$624.30		$667.6981	$667.71	$667.70	$667.70