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	$133.28	3.850%	$138.4113	$138.41	$138.40	$138.40
Purchase #2	$175.70	11.777%	$196.3922	$196.39	$196.40	$196.40
Purchase #3	$247.90	13.518%	$281.4111	$281.41	$281.40	$281.40
Purchase #4	$228.51	6.209%	$242.6982	$242.70	$242.70	$242.70
Purchase #5	$67.43	5.567%	$71.1838	$71.18	$71.20	$71.20
Purchase #6	$157.96	6.697%	$168.5386	$168.54	$168.55	$168.50
Purchase #7	$178.73	12.163%	$200.4689	$200.47	$200.45	$200.50
7 purchase totals =	$1,189.51		$1,299.1041	$1,299.10	$1,299.10	$1,299.10