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	$113.45	7.303%	$121.7353	$121.74	$121.75	$121.70
Purchase #2	$80.32	11.244%	$89.3512	$89.35	$89.35	$89.40
Purchase #3	$209.35	12.314%	$235.1294	$235.13	$235.15	$235.10
Purchase #4	$19.33	11.266%	$21.5077	$21.51	$21.50	$21.50
Purchase #5	$37.36	13.853%	$42.5355	$42.54	$42.55	$42.50
Purchase #6	$33.46	4.872%	$35.0902	$35.09	$35.10	$35.10
Purchase #7	$226.83	10.503%	$250.654	$250.65	$250.65	$250.70
7 purchase totals =	$720.10		$796.0033	$796.01	$796.05	$796.00