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	$42.67	6.662%	$45.5127	$45.51	$45.50	$45.50
Purchase #2	$77.45	4.632%	$81.0375	$81.04	$81.05	$81.00
Purchase #3	$102.45	4.277%	$106.8318	$106.83	$106.85	$106.80
Purchase #4	$63.66	11.328%	$70.8714	$70.87	$70.85	$70.90
Purchase #5	$190.90	9.821%	$209.6483	$209.65	$209.65	$209.60
Purchase #6	$120.35	10.604%	$133.1119	$133.11	$133.10	$133.10
Purchase #7	$69.78	11.179%	$77.5807	$77.58	$77.60	$77.60
7 purchase totals =	$667.26		$724.5943	$724.59	$724.60	$724.50