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	$78.76	8.619%	$85.5483	$85.55	$85.55	$85.50
Purchase #2	$19.69	11.578%	$21.9697	$21.97	$21.95	$22.00
Purchase #3	$46.72	13.431%	$52.995	$53.00	$53.00	$53.00
Purchase #4	$79.98	13.657%	$90.9029	$90.90	$90.90	$90.90
Purchase #5	$238.94	12.512%	$268.8362	$268.84	$268.85	$268.80
Purchase #6	$82.51	12.273%	$92.6365	$92.64	$92.65	$92.60
Purchase #7	$27.38	4.366%	$28.5754	$28.58	$28.60	$28.60
7 purchase totals =	$573.98		$641.4640	$641.48	$641.50	$641.40