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	$12.45	4.201%	$12.973	$12.97	$12.95	$13.00
Purchase #2	$200.32	10.440%	$221.2334	$221.23	$221.25	$221.20
Purchase #3	$28.87	11.767%	$32.2671	$32.27	$32.25	$32.30
Purchase #4	$64.27	4.311%	$67.0407	$67.04	$67.05	$67.00
Purchase #5	$104.36	9.853%	$114.6426	$114.64	$114.65	$114.60
Purchase #6	$49.39	13.812%	$56.2117	$56.21	$56.20	$56.20
Purchase #7	$150.36	9.785%	$165.0727	$165.07	$165.05	$165.10
7 purchase totals =	$610.02		$669.4412	$669.43	$669.40	$669.40