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	$238.49	7.715%	$256.8895	$256.89	$256.90	$256.90
Purchase #2	$230.52	8.677%	$250.5222	$250.52	$250.50	$250.50
Purchase #3	$166.57	9.102%	$181.7312	$181.73	$181.75	$181.70
Purchase #4	$173.91	13.107%	$196.7044	$196.70	$196.70	$196.70
Purchase #5	$234.87	9.275%	$256.6542	$256.65	$256.65	$256.70
Purchase #6	$86.47	6.185%	$91.8182	$91.82	$91.80	$91.80
Purchase #7	$35.84	9.151%	$39.1197	$39.12	$39.10	$39.10
7 purchase totals =	$1,166.67		$1,273.4394	$1,273.43	$1,273.40	$1,273.40