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	$142.73	9.737%	$156.6276	$156.63	$156.65	$156.60
Purchase #2	$75.92	6.317%	$80.7159	$80.72	$80.70	$80.70
Purchase #3	$144.42	4.356%	$150.7109	$150.71	$150.70	$150.70
Purchase #4	$86.41	3.792%	$89.6867	$89.69	$89.70	$89.70
Purchase #5	$78.44	7.275%	$84.1465	$84.15	$84.15	$84.10
Purchase #6	$190.78	13.795%	$217.0981	$217.10	$217.10	$217.10
Purchase #7	$25.75	11.356%	$28.6742	$28.67	$28.65	$28.70
7 purchase totals =	$744.45		$807.6599	$807.67	$807.65	$807.60