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	$232.30	5.408%	$244.8628	$244.86	$244.85	$244.90
Purchase #2	$88.60	3.373%	$91.5885	$91.59	$91.60	$91.60
Purchase #3	$213.48	11.505%	$238.0409	$238.04	$238.05	$238.00
Purchase #4	$18.58	7.400%	$19.9549	$19.95	$19.95	$20.00
Purchase #5	$38.72	10.738%	$42.8778	$42.88	$42.90	$42.90
Purchase #6	$136.82	9.799%	$150.227	$150.23	$150.25	$150.20
Purchase #7	$100.72	11.716%	$112.5204	$112.52	$112.50	$112.50
7 purchase totals =	$829.22		$900.0723	$900.07	$900.10	$900.10