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	$138.89	12.860%	$156.7513	$156.75	$156.75	$156.80
Purchase #2	$232.32	13.701%	$264.1502	$264.15	$264.15	$264.20
Purchase #3	$30.28	4.200%	$31.5518	$31.55	$31.55	$31.60
Purchase #4	$84.39	9.625%	$92.5125	$92.51	$92.50	$92.50
Purchase #5	$37.25	9.598%	$40.8253	$40.83	$40.85	$40.80
Purchase #6	$47.92	6.473%	$51.0219	$51.02	$51.00	$51.00
Purchase #7	$85.51	5.273%	$90.0189	$90.02	$90.00	$90.00
7 purchase totals =	$656.56		$726.8319	$726.83	$726.80	$726.90