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	$80.38	4.403%	$83.9191	$83.92	$83.90	$83.90
Purchase #2	$95.64	8.290%	$103.5686	$103.57	$103.55	$103.60
Purchase #3	$161.52	11.626%	$180.2983	$180.30	$180.30	$180.30
Purchase #4	$150.46	4.754%	$157.6129	$157.61	$157.60	$157.60
Purchase #5	$7.38	5.630%	$7.7955	$7.80	$7.80	$7.80
Purchase #6	$115.61	6.524%	$123.1524	$123.15	$123.15	$123.20
Purchase #7	$61.59	6.428%	$65.549	$65.55	$65.55	$65.50
7 purchase totals =	$672.58		$721.8958	$721.90	$721.85	$721.90