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	$33.69	13.793%	$38.3369	$38.34	$38.35	$38.30
Purchase #2	$65.69	10.686%	$72.7096	$72.71	$72.70	$72.70
Purchase #3	$73.42	10.182%	$80.8956	$80.90	$80.90	$80.90
Purchase #4	$223.57	10.572%	$247.2058	$247.21	$247.20	$247.20
Purchase #5	$22.60	11.231%	$25.1382	$25.14	$25.15	$25.10
Purchase #6	$154.53	12.667%	$174.1043	$174.10	$174.10	$174.10
Purchase #7	$39.76	9.659%	$43.6004	$43.60	$43.60	$43.60
7 purchase totals =	$613.26		$681.9908	$682.00	$682.00	$681.90