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	$97.32	3.585%	$100.8089	$100.81	$100.80	$100.80
Purchase #2	$205.90	8.354%	$223.1009	$223.10	$223.10	$223.10
Purchase #3	$19.86	7.142%	$21.2784	$21.28	$21.30	$21.30
Purchase #4	$197.52	11.460%	$220.1558	$220.16	$220.15	$220.20
Purchase #5	$185.88	7.524%	$199.8656	$199.87	$199.85	$199.90
Purchase #6	$214.26	4.357%	$223.5953	$223.60	$223.60	$223.60
Purchase #7	$136.83	4.434%	$142.897	$142.90	$142.90	$142.90
7 purchase totals =	$1,057.57		$1,131.7019	$1,131.72	$1,131.70	$1,131.80