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	$12.36	4.377%	$12.901	$12.90	$12.90	$12.90
Purchase #2	$31.39	4.191%	$32.7056	$32.71	$32.70	$32.70
Purchase #3	$54.81	8.261%	$59.3379	$59.34	$59.35	$59.30
Purchase #4	$203.90	8.670%	$221.5781	$221.58	$221.60	$221.60
Purchase #5	$225.79	5.577%	$238.3823	$238.38	$238.40	$238.40
Purchase #6	$125.61	6.786%	$134.1339	$134.13	$134.15	$134.10
Purchase #7	$100.96	9.387%	$110.4371	$110.44	$110.45	$110.40
7 purchase totals =	$754.82		$809.4759	$809.48	$809.55	$809.40