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	$84.84	5.766%	$89.7319	$89.73	$89.75	$89.70
Purchase #2	$61.59	13.420%	$69.8554	$69.86	$69.85	$69.90
Purchase #3	$80.29	12.632%	$90.4322	$90.43	$90.45	$90.40
Purchase #4	$163.53	4.826%	$171.422	$171.42	$171.40	$171.40
Purchase #5	$218.27	9.824%	$239.7128	$239.71	$239.70	$239.70
Purchase #6	$149.82	12.308%	$168.2598	$168.26	$168.25	$168.30
Purchase #7	$133.44	6.396%	$141.9748	$141.97	$141.95	$142.00
7 purchase totals =	$891.78		$971.3889	$971.38	$971.35	$971.40