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	$128.33	8.485%	$139.2188	$139.22	$139.20	$139.20
Purchase #2	$144.41	4.577%	$151.0196	$151.02	$151.00	$151.00
Purchase #3	$87.90	6.480%	$93.5959	$93.60	$93.60	$93.60
Purchase #4	$243.72	8.701%	$264.9261	$264.93	$264.95	$264.90
Purchase #5	$225.95	6.776%	$241.2604	$241.26	$241.25	$241.30
Purchase #6	$131.83	6.442%	$140.3225	$140.32	$140.30	$140.30
Purchase #7	$18.45	9.571%	$20.2158	$20.22	$20.20	$20.20
7 purchase totals =	$980.59		$1,050.5591	$1,050.57	$1,050.50	$1,050.50