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	$33.43	4.809%	$35.0376	$35.04	$35.05	$35.00
Purchase #2	$128.48	7.794%	$138.4937	$138.49	$138.50	$138.50
Purchase #3	$85.97	4.704%	$90.014	$90.01	$90.00	$90.00
Purchase #4	$93.58	8.182%	$101.2367	$101.24	$101.25	$101.20
Purchase #5	$133.78	12.565%	$150.5895	$150.59	$150.60	$150.60
Purchase #6	$62.67	11.860%	$70.1027	$70.10	$70.10	$70.10
Purchase #7	$232.52	5.797%	$245.9992	$246.00	$246.00	$246.00
7 purchase totals =	$770.43		$831.4734	$831.47	$831.50	$831.40