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	$128.86	12.873%	$145.4481	$145.45	$145.45	$145.40
Purchase #2	$143.90	10.585%	$159.1318	$159.13	$159.15	$159.10
Purchase #3	$60.78	9.313%	$66.4404	$66.44	$66.45	$66.40
Purchase #4	$61.30	8.836%	$66.7165	$66.72	$66.70	$66.70
Purchase #5	$227.83	12.120%	$255.443	$255.44	$255.45	$255.40
Purchase #6	$24.77	8.507%	$26.8772	$26.88	$26.90	$26.90
Purchase #7	$89.48	10.579%	$98.9461	$98.95	$98.95	$98.90
7 purchase totals =	$736.92		$819.0031	$819.01	$819.05	$818.80