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	$25.47	7.164%	$27.2947	$27.29	$27.30	$27.30
Purchase #2	$241.32	6.385%	$256.7283	$256.73	$256.75	$256.70
Purchase #3	$111.83	4.751%	$117.143	$117.14	$117.15	$117.10
Purchase #4	$13.89	7.184%	$14.8879	$14.89	$14.90	$14.90
Purchase #5	$77.58	4.214%	$80.8492	$80.85	$80.85	$80.80
Purchase #6	$199.95	8.447%	$216.8398	$216.84	$216.85	$216.80
Purchase #7	$121.57	5.196%	$127.8868	$127.89	$127.90	$127.90
7 purchase totals =	$791.61		$841.6297	$841.63	$841.70	$841.50