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	$19.53	11.297%	$21.7363	$21.74	$21.75	$21.70
Purchase #2	$175.76	13.356%	$199.2345	$199.23	$199.25	$199.20
Purchase #3	$62.76	6.781%	$67.0158	$67.02	$67.00	$67.00
Purchase #4	$32.65	8.342%	$35.3737	$35.37	$35.35	$35.40
Purchase #5	$241.89	8.504%	$262.4603	$262.46	$262.45	$262.50
Purchase #6	$66.80	10.119%	$73.5595	$73.56	$73.55	$73.60
Purchase #7	$151.88	11.286%	$169.0212	$169.02	$169.00	$169.00
7 purchase totals =	$751.27		$828.4013	$828.40	$828.35	$828.40