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	$80.51	4.190%	$83.8834	$83.88	$83.90	$83.90
Purchase #2	$250.76	13.580%	$284.8132	$284.81	$284.80	$284.80
Purchase #3	$114.57	5.466%	$120.8324	$120.83	$120.85	$120.80
Purchase #4	$186.53	11.698%	$208.3503	$208.35	$208.35	$208.40
Purchase #5	$91.89	11.659%	$102.6035	$102.60	$102.60	$102.60
Purchase #6	$39.66	8.358%	$42.9748	$42.97	$42.95	$43.00
Purchase #7	$227.43	9.114%	$248.158	$248.16	$248.15	$248.20
7 purchase totals =	$991.35		$1,091.6156	$1,091.60	$1,091.60	$1,091.70