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	$35.80	13.774%	$40.7311	$40.73	$40.75	$40.70
Purchase #2	$174.45	6.253%	$185.3584	$185.36	$185.35	$185.40
Purchase #3	$48.92	9.296%	$53.4676	$53.47	$53.45	$53.50
Purchase #4	$32.59	8.233%	$35.2731	$35.27	$35.25	$35.30
Purchase #5	$27.67	8.519%	$30.0272	$30.03	$30.05	$30.00
Purchase #6	$227.64	10.183%	$250.8206	$250.82	$250.80	$250.80
Purchase #7	$32.43	12.762%	$36.5687	$36.57	$36.55	$36.60
7 purchase totals =	$579.50		$632.2467	$632.25	$632.20	$632.30