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	$113.51	3.114%	$117.0447	$117.04	$117.05	$117.00
Purchase #2	$49.91	11.411%	$55.6052	$55.61	$55.60	$55.60
Purchase #3	$238.31	10.319%	$262.9012	$262.90	$262.90	$262.90
Purchase #4	$68.89	11.690%	$76.9432	$76.94	$76.95	$76.90
Purchase #5	$66.78	7.688%	$71.914	$71.91	$71.90	$71.90
Purchase #6	$173.74	3.141%	$179.1972	$179.20	$179.20	$179.20
Purchase #7	$148.55	12.654%	$167.3475	$167.35	$167.35	$167.30
7 purchase totals =	$859.69		$930.9530	$930.95	$930.95	$930.80