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	$19.25	9.257%	$21.032	$21.03	$21.05	$21.00
Purchase #2	$126.78	13.782%	$144.2528	$144.25	$144.25	$144.30
Purchase #3	$142.26	9.319%	$155.5172	$155.52	$155.50	$155.50
Purchase #4	$144.71	10.150%	$159.3981	$159.40	$159.40	$159.40
Purchase #5	$20.73	5.596%	$21.8901	$21.89	$21.90	$21.90
Purchase #6	$120.40	3.741%	$124.9042	$124.90	$124.90	$124.90
Purchase #7	$133.79	5.294%	$140.8728	$140.87	$140.85	$140.90
7 purchase totals =	$707.92		$767.8672	$767.86	$767.85	$767.90