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	$84.38	7.714%	$90.8891	$90.89	$90.90	$90.90
Purchase #2	$228.27	4.640%	$238.8617	$238.86	$238.85	$238.90
Purchase #3	$187.50	12.623%	$211.1681	$211.17	$211.15	$211.20
Purchase #4	$95.36	10.456%	$105.3308	$105.33	$105.35	$105.30
Purchase #5	$74.77	7.573%	$80.4323	$80.43	$80.45	$80.40
Purchase #6	$87.64	9.789%	$96.2191	$96.22	$96.20	$96.20
Purchase #7	$201.49	4.452%	$210.4603	$210.46	$210.45	$210.50
7 purchase totals =	$959.41		$1,033.3614	$1,033.36	$1,033.35	$1,033.40