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	$69.31	12.669%	$78.0909	$78.09	$78.10	$78.10
Purchase #2	$35.46	5.720%	$37.4883	$37.49	$37.50	$37.50
Purchase #3	$153.53	8.401%	$166.4281	$166.43	$166.45	$166.40
Purchase #4	$6.57	11.459%	$7.3229	$7.32	$7.30	$7.30
Purchase #5	$150.98	3.378%	$156.0801	$156.08	$156.10	$156.10
Purchase #6	$154.26	8.238%	$166.9679	$166.97	$166.95	$167.00
Purchase #7	$212.26	6.149%	$225.3119	$225.31	$225.30	$225.30
7 purchase totals =	$782.37		$837.6901	$837.69	$837.70	$837.70