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	$228.66	9.287%	$249.8957	$249.90	$249.90	$249.90
Purchase #2	$117.26	12.159%	$131.5176	$131.52	$131.50	$131.50
Purchase #3	$202.44	13.374%	$229.5143	$229.51	$229.50	$229.50
Purchase #4	$71.98	8.841%	$78.3438	$78.34	$78.35	$78.30
Purchase #5	$42.81	4.683%	$44.8148	$44.81	$44.80	$44.80
Purchase #6	$52.32	6.186%	$55.5565	$55.56	$55.55	$55.60
Purchase #7	$92.33	10.701%	$102.2102	$102.21	$102.20	$102.20
7 purchase totals =	$807.80		$891.8529	$891.85	$891.80	$891.80