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	$183.69	13.574%	$208.6241	$208.62	$208.60	$208.60
Purchase #2	$200.91	11.411%	$223.8358	$223.84	$223.85	$223.80
Purchase #3	$81.86	9.616%	$89.7317	$89.73	$89.75	$89.70
Purchase #4	$15.97	13.119%	$18.0651	$18.07	$18.05	$18.10
Purchase #5	$40.50	11.204%	$45.0376	$45.04	$45.05	$45.00
Purchase #6	$33.86	6.116%	$35.9309	$35.93	$35.95	$35.90
Purchase #7	$221.56	3.157%	$228.5546	$228.55	$228.55	$228.60
7 purchase totals =	$778.35		$849.7798	$849.78	$849.80	$849.70