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	$18.76	6.411%	$19.9627	$19.96	$19.95	$20.00
Purchase #2	$208.80	6.472%	$222.3135	$222.31	$222.30	$222.30
Purchase #3	$151.63	6.483%	$161.4602	$161.46	$161.45	$161.50
Purchase #4	$29.62	9.126%	$32.3231	$32.32	$32.30	$32.30
Purchase #5	$96.69	3.678%	$100.2463	$100.25	$100.25	$100.20
Purchase #6	$81.91	7.386%	$87.9599	$87.96	$87.95	$88.00
Purchase #7	$74.79	4.582%	$78.2169	$78.22	$78.20	$78.20
7 purchase totals =	$662.20		$702.4826	$702.48	$702.40	$702.50