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	$73.85	4.388%	$77.0905	$77.09	$77.10	$77.10
Purchase #2	$201.49	10.682%	$223.0132	$223.01	$223.00	$223.00
Purchase #3	$193.25	13.406%	$219.1571	$219.16	$219.15	$219.20
Purchase #4	$92.82	6.283%	$98.6519	$98.65	$98.65	$98.70
Purchase #5	$31.81	3.871%	$33.0414	$33.04	$33.05	$33.00
Purchase #6	$89.88	8.610%	$97.6187	$97.62	$97.60	$97.60
Purchase #7	$77.72	10.481%	$85.8658	$85.87	$85.85	$85.90
7 purchase totals =	$760.82		$834.4386	$834.44	$834.40	$834.50