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	$31.64	12.397%	$35.5624	$35.56	$35.55	$35.60
Purchase #2	$76.35	8.116%	$82.5466	$82.55	$82.55	$82.50
Purchase #3	$195.41	13.800%	$222.3766	$222.38	$222.40	$222.40
Purchase #4	$40.29	4.335%	$42.0366	$42.04	$42.05	$42.00
Purchase #5	$209.27	4.377%	$218.4297	$218.43	$218.45	$218.40
Purchase #6	$170.80	4.222%	$178.0112	$178.01	$178.00	$178.00
Purchase #7	$9.83	5.827%	$10.4028	$10.40	$10.40	$10.40
7 purchase totals =	$733.59		$789.3659	$789.37	$789.40	$789.30