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	$40.93	4.454%	$42.753	$42.75	$42.75	$42.80
Purchase #2	$116.57	4.695%	$122.043	$122.04	$122.05	$122.00
Purchase #3	$20.85	3.349%	$21.5483	$21.55	$21.55	$21.50
Purchase #4	$205.86	11.380%	$229.2869	$229.29	$229.30	$229.30
Purchase #5	$109.60	6.150%	$116.3404	$116.34	$116.35	$116.30
Purchase #6	$195.77	3.450%	$202.5241	$202.52	$202.50	$202.50
Purchase #7	$91.85	7.792%	$99.007	$99.01	$99.00	$99.00
7 purchase totals =	$781.43		$833.5027	$833.50	$833.50	$833.40