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	$147.88	12.275%	$166.0323	$166.03	$166.05	$166.00
Purchase #2	$73.46	8.482%	$79.6909	$79.69	$79.70	$79.70
Purchase #3	$35.82	5.511%	$37.794	$37.79	$37.80	$37.80
Purchase #4	$241.77	7.589%	$260.1179	$260.12	$260.10	$260.10
Purchase #5	$117.34	5.389%	$123.6635	$123.66	$123.65	$123.70
Purchase #6	$238.40	10.231%	$262.7907	$262.79	$262.80	$262.80
Purchase #7	$77.86	13.628%	$88.4708	$88.47	$88.45	$88.50
7 purchase totals =	$932.53		$1,018.5601	$1,018.55	$1,018.55	$1,018.60