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	$82.83	8.323%	$89.7239	$89.72	$89.70	$89.70
Purchase #2	$134.48	9.272%	$146.949	$146.95	$146.95	$146.90
Purchase #3	$12.91	7.387%	$13.8637	$13.86	$13.85	$13.90
Purchase #4	$206.86	7.423%	$222.2152	$222.22	$222.20	$222.20
Purchase #5	$201.77	10.631%	$223.2202	$223.22	$223.20	$223.20
Purchase #6	$122.57	9.285%	$133.9506	$133.95	$133.95	$134.00
Purchase #7	$249.41	3.471%	$258.067	$258.07	$258.05	$258.10
7 purchase totals =	$1,010.83		$1,087.9896	$1,087.99	$1,087.90	$1,088.00