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	$140.87	3.289%	$145.5032	$145.50	$145.50	$145.50
Purchase #2	$117.63	5.587%	$124.202	$124.20	$124.20	$124.20
Purchase #3	$175.32	9.572%	$192.1016	$192.10	$192.10	$192.10
Purchase #4	$200.28	11.401%	$223.1139	$223.11	$223.10	$223.10
Purchase #5	$79.79	12.648%	$89.8818	$89.88	$89.90	$89.90
Purchase #6	$78.94	4.847%	$82.7662	$82.77	$82.75	$82.80
Purchase #7	$57.88	3.481%	$59.8948	$59.89	$59.90	$59.90
7 purchase totals =	$850.71		$917.4635	$917.45	$917.45	$917.50