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	$247.99	9.203%	$270.8125	$270.81	$270.80	$270.80
Purchase #2	$164.26	4.284%	$171.2969	$171.30	$171.30	$171.30
Purchase #3	$114.51	4.603%	$119.7809	$119.78	$119.80	$119.80
Purchase #4	$50.94	8.785%	$55.4151	$55.42	$55.40	$55.40
Purchase #5	$75.59	3.642%	$78.343	$78.34	$78.35	$78.30
Purchase #6	$158.27	12.150%	$177.4998	$177.50	$177.50	$177.50
Purchase #7	$136.41	7.181%	$146.2056	$146.21	$146.20	$146.20
7 purchase totals =	$947.97		$1,019.3538	$1,019.36	$1,019.35	$1,019.30