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	$123.86	5.429%	$130.5844	$130.58	$130.60	$130.60
Purchase #2	$59.29	11.565%	$66.1469	$66.15	$66.15	$66.10
Purchase #3	$119.59	12.755%	$134.8437	$134.84	$134.85	$134.80
Purchase #4	$85.28	12.825%	$96.2172	$96.22	$96.20	$96.20
Purchase #5	$214.36	6.605%	$228.5185	$228.52	$228.50	$228.50
Purchase #6	$59.31	4.400%	$61.9196	$61.92	$61.90	$61.90
Purchase #7	$123.85	13.488%	$140.5549	$140.55	$140.55	$140.60
7 purchase totals =	$785.54		$858.7852	$858.78	$858.75	$858.70