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	$148.47	4.665%	$155.3961	$155.40	$155.40	$155.40
Purchase #2	$183.69	10.526%	$203.0252	$203.03	$203.05	$203.00
Purchase #3	$24.36	8.310%	$26.3843	$26.38	$26.40	$26.40
Purchase #4	$71.41	10.544%	$78.9395	$78.94	$78.95	$78.90
Purchase #5	$35.73	5.588%	$37.7266	$37.73	$37.75	$37.70
Purchase #6	$79.80	13.481%	$90.5578	$90.56	$90.55	$90.60
Purchase #7	$44.50	4.194%	$46.3663	$46.37	$46.35	$46.40
7 purchase totals =	$587.96		$638.3958	$638.41	$638.45	$638.40