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	$74.39	8.750%	$80.8991	$80.90	$80.90	$80.90
Purchase #2	$214.43	4.597%	$224.2873	$224.29	$224.30	$224.30
Purchase #3	$112.94	9.266%	$123.405	$123.41	$123.40	$123.40
Purchase #4	$238.50	12.482%	$268.2696	$268.27	$268.25	$268.30
Purchase #5	$141.87	8.187%	$153.4849	$153.48	$153.50	$153.50
Purchase #6	$97.96	6.291%	$104.1227	$104.12	$104.10	$104.10
Purchase #7	$142.42	8.866%	$155.047	$155.05	$155.05	$155.00
7 purchase totals =	$1,022.51		$1,109.5156	$1,109.52	$1,109.50	$1,109.50