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	$75.77	5.704%	$80.0919	$80.09	$80.10	$80.10
Purchase #2	$99.65	3.467%	$103.1049	$103.10	$103.10	$103.10
Purchase #3	$187.64	4.421%	$195.9356	$195.94	$195.95	$195.90
Purchase #4	$226.81	5.179%	$238.5565	$238.56	$238.55	$238.60
Purchase #5	$73.75	6.102%	$78.2502	$78.25	$78.25	$78.30
Purchase #6	$242.51	4.774%	$254.0874	$254.09	$254.10	$254.10
Purchase #7	$86.81	4.198%	$90.4543	$90.45	$90.45	$90.50
7 purchase totals =	$992.94		$1,040.4808	$1,040.48	$1,040.50	$1,040.60