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	$84.95	5.873%	$89.9391	$89.94	$89.95	$89.90
Purchase #2	$162.60	13.810%	$185.0551	$185.06	$185.05	$185.10
Purchase #3	$155.91	12.220%	$174.9622	$174.96	$174.95	$175.00
Purchase #4	$174.72	3.329%	$180.5364	$180.54	$180.55	$180.50
Purchase #5	$229.31	11.413%	$255.4812	$255.48	$255.50	$255.50
Purchase #6	$163.31	4.252%	$170.2539	$170.25	$170.25	$170.30
Purchase #7	$213.25	4.306%	$222.4325	$222.43	$222.45	$222.40
7 purchase totals =	$1,184.05		$1,278.6604	$1,278.66	$1,278.70	$1,278.70