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	$79.79	13.849%	$90.8401	$90.84	$90.85	$90.80
Purchase #2	$118.56	9.721%	$130.0852	$130.09	$130.10	$130.10
Purchase #3	$128.81	11.476%	$143.5922	$143.59	$143.60	$143.60
Purchase #4	$187.54	7.126%	$200.9041	$200.90	$200.90	$200.90
Purchase #5	$24.52	12.173%	$27.5048	$27.50	$27.50	$27.50
Purchase #6	$231.56	5.133%	$243.446	$243.45	$243.45	$243.40
Purchase #7	$142.43	7.343%	$152.8886	$152.89	$152.90	$152.90
7 purchase totals =	$913.21		$989.2610	$989.26	$989.30	$989.20