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	$53.95	3.611%	$55.8981	$55.90	$55.90	$55.90
Purchase #2	$39.39	7.749%	$42.4423	$42.44	$42.45	$42.40
Purchase #3	$138.29	8.861%	$150.5439	$150.54	$150.55	$150.50
Purchase #4	$20.90	10.502%	$23.0949	$23.09	$23.10	$23.10
Purchase #5	$19.68	12.409%	$22.1221	$22.12	$22.10	$22.10
Purchase #6	$43.36	4.657%	$45.3793	$45.38	$45.40	$45.40
Purchase #7	$172.79	9.443%	$189.1066	$189.11	$189.10	$189.10
7 purchase totals =	$488.36		$528.5872	$528.58	$528.60	$528.50