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	$28.27	11.673%	$31.57	$31.57	$31.55	$31.60
Purchase #2	$37.55	8.113%	$40.5964	$40.60	$40.60	$40.60
Purchase #3	$197.39	9.845%	$216.823	$216.82	$216.80	$216.80
Purchase #4	$221.50	12.419%	$249.0081	$249.01	$249.00	$249.00
Purchase #5	$150.37	4.782%	$157.5607	$157.56	$157.55	$157.60
Purchase #6	$134.84	6.763%	$143.9592	$143.96	$143.95	$144.00
Purchase #7	$145.80	12.551%	$164.0994	$164.10	$164.10	$164.10
7 purchase totals =	$915.72		$1,003.6168	$1,003.62	$1,003.55	$1,003.70