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	$247.52	13.465%	$280.8486	$280.85	$280.85	$280.80
Purchase #2	$140.49	12.513%	$158.0695	$158.07	$158.05	$158.10
Purchase #3	$172.30	11.129%	$191.4753	$191.48	$191.50	$191.50
Purchase #4	$235.53	8.357%	$255.2132	$255.21	$255.20	$255.20
Purchase #5	$180.83	11.340%	$201.3361	$201.34	$201.35	$201.30
Purchase #6	$208.53	11.789%	$233.1136	$233.11	$233.10	$233.10
Purchase #7	$73.82	10.174%	$81.3304	$81.33	$81.35	$81.30
7 purchase totals =	$1,259.02		$1,401.3867	$1,401.39	$1,401.40	$1,401.30