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	$47.87	10.674%	$52.9796	$52.98	$53.00	$53.00
Purchase #2	$240.76	10.403%	$265.8063	$265.81	$265.80	$265.80
Purchase #3	$135.51	5.761%	$143.3167	$143.32	$143.30	$143.30
Purchase #4	$230.83	3.466%	$238.8306	$238.83	$238.85	$238.80
Purchase #5	$5.34	10.638%	$5.9081	$5.91	$5.90	$5.90
Purchase #6	$38.82	9.485%	$42.5021	$42.50	$42.50	$42.50
Purchase #7	$85.92	6.378%	$91.4	$91.40	$91.40	$91.40
7 purchase totals =	$785.05		$840.7434	$840.75	$840.75	$840.70