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	$182.42	3.824%	$189.3957	$189.40	$189.40	$189.40
Purchase #2	$75.31	4.772%	$78.9038	$78.90	$78.90	$78.90
Purchase #3	$164.89	13.770%	$187.5954	$187.60	$187.60	$187.60
Purchase #4	$100.35	10.288%	$110.674	$110.67	$110.65	$110.70
Purchase #5	$235.38	7.572%	$253.203	$253.20	$253.20	$253.20
Purchase #6	$214.49	3.454%	$221.8985	$221.90	$221.90	$221.90
Purchase #7	$37.40	12.804%	$42.1887	$42.19	$42.20	$42.20
7 purchase totals =	$1,010.24		$1,083.8591	$1,083.86	$1,083.85	$1,083.90