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	$31.92	11.489%	$35.5873	$35.59	$35.60	$35.60
Purchase #2	$153.29	10.135%	$168.8259	$168.83	$168.85	$168.80
Purchase #3	$96.25	8.687%	$104.6112	$104.61	$104.60	$104.60
Purchase #4	$130.72	9.428%	$143.0443	$143.04	$143.05	$143.00
Purchase #5	$188.80	4.230%	$196.7862	$196.79	$196.80	$196.80
Purchase #6	$117.41	10.298%	$129.5009	$129.50	$129.50	$129.50
Purchase #7	$122.80	13.761%	$139.6985	$139.70	$139.70	$139.70
7 purchase totals =	$841.19		$918.0543	$918.06	$918.10	$918.00