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	$73.82	9.293%	$80.6801	$80.68	$80.70	$80.70
Purchase #2	$135.69	12.387%	$152.4979	$152.50	$152.50	$152.50
Purchase #3	$214.79	10.421%	$237.1733	$237.17	$237.15	$237.20
Purchase #4	$35.50	6.595%	$37.8412	$37.84	$37.85	$37.80
Purchase #5	$114.70	7.669%	$123.4963	$123.50	$123.50	$123.50
Purchase #6	$164.79	12.586%	$185.5305	$185.53	$185.55	$185.50
Purchase #7	$7.93	7.248%	$8.5048	$8.50	$8.50	$8.50
7 purchase totals =	$747.22		$825.7241	$825.72	$825.75	$825.70