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	$57.88	3.448%	$59.8757	$59.88	$59.90	$59.90
Purchase #2	$52.53	13.384%	$59.5606	$59.56	$59.55	$59.60
Purchase #3	$90.59	10.370%	$99.9842	$99.98	$100.00	$100.00
Purchase #4	$146.94	9.691%	$161.18	$161.18	$161.20	$161.20
Purchase #5	$158.73	3.833%	$164.8141	$164.81	$164.80	$164.80
Purchase #6	$198.43	8.861%	$216.0129	$216.01	$216.00	$216.00
Purchase #7	$223.79	12.162%	$251.0073	$251.01	$251.00	$251.00
7 purchase totals =	$928.89		$1,012.4348	$1,012.43	$1,012.45	$1,012.50