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	$75.84	5.532%	$80.0355	$80.04	$80.05	$80.00
Purchase #2	$163.52	3.665%	$169.513	$169.51	$169.50	$169.50
Purchase #3	$40.33	12.624%	$45.4213	$45.42	$45.40	$45.40
Purchase #4	$154.50	9.165%	$168.6599	$168.66	$168.65	$168.70
Purchase #5	$46.39	11.848%	$51.8863	$51.89	$51.90	$51.90
Purchase #6	$246.58	12.426%	$277.22	$277.22	$277.20	$277.20
Purchase #7	$233.81	4.162%	$243.5412	$243.54	$243.55	$243.50
7 purchase totals =	$960.97		$1,036.2772	$1,036.28	$1,036.25	$1,036.20