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	$240.44	6.112%	$255.1357	$255.14	$255.15	$255.10
Purchase #2	$219.54	3.140%	$226.4336	$226.43	$226.45	$226.40
Purchase #3	$39.53	7.866%	$42.6394	$42.64	$42.65	$42.60
Purchase #4	$110.80	10.126%	$122.0196	$122.02	$122.00	$122.00
Purchase #5	$92.84	5.827%	$98.2498	$98.25	$98.25	$98.20
Purchase #6	$189.59	7.843%	$204.4595	$204.46	$204.45	$204.50
Purchase #7	$50.89	7.748%	$54.833	$54.83	$54.85	$54.80
7 purchase totals =	$943.63		$1,003.7706	$1,003.77	$1,003.80	$1,003.60