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	$77.48	9.821%	$85.0893	$85.09	$85.10	$85.10
Purchase #2	$239.80	4.373%	$250.2865	$250.29	$250.30	$250.30
Purchase #3	$51.51	6.647%	$54.9339	$54.93	$54.95	$54.90
Purchase #4	$226.96	12.866%	$256.1607	$256.16	$256.15	$256.20
Purchase #5	$108.73	10.598%	$120.2532	$120.25	$120.25	$120.30
Purchase #6	$56.54	4.352%	$59.0006	$59.00	$59.00	$59.00
Purchase #7	$72.81	10.715%	$80.6116	$80.61	$80.60	$80.60
7 purchase totals =	$833.83		$906.3358	$906.33	$906.35	$906.40