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	$52.90	12.171%	$59.3385	$59.34	$59.35	$59.30
Purchase #2	$151.81	8.416%	$164.5863	$164.59	$164.60	$164.60
Purchase #3	$89.29	10.196%	$98.394	$98.39	$98.40	$98.40
Purchase #4	$22.59	13.789%	$25.7049	$25.70	$25.70	$25.70
Purchase #5	$95.33	10.295%	$105.1442	$105.14	$105.15	$105.10
Purchase #6	$28.69	9.570%	$31.4356	$31.44	$31.45	$31.40
Purchase #7	$29.37	9.659%	$32.2068	$32.21	$32.20	$32.20
7 purchase totals =	$469.98		$516.8103	$516.81	$516.85	$516.70