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	$78.43	3.158%	$80.9068	$80.91	$80.90	$80.90
Purchase #2	$241.50	12.689%	$272.1439	$272.14	$272.15	$272.10
Purchase #3	$203.95	3.488%	$211.0638	$211.06	$211.05	$211.10
Purchase #4	$122.47	7.570%	$131.741	$131.74	$131.75	$131.70
Purchase #5	$104.60	13.306%	$118.5181	$118.52	$118.50	$118.50
Purchase #6	$37.53	11.618%	$41.8902	$41.89	$41.90	$41.90
Purchase #7	$112.39	5.572%	$118.6524	$118.65	$118.65	$118.70
7 purchase totals =	$900.87		$974.9162	$974.91	$974.90	$974.90