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	$105.97	13.210%	$119.9686	$119.97	$119.95	$120.00
Purchase #2	$165.55	7.218%	$177.4994	$177.50	$177.50	$177.50
Purchase #3	$54.90	11.360%	$61.1366	$61.14	$61.15	$61.10
Purchase #4	$14.75	6.209%	$15.6658	$15.67	$15.65	$15.70
Purchase #5	$150.79	11.343%	$167.8941	$167.89	$167.90	$167.90
Purchase #6	$119.41	7.636%	$128.5281	$128.53	$128.55	$128.50
Purchase #7	$208.46	6.312%	$221.618	$221.62	$221.60	$221.60
7 purchase totals =	$819.83		$892.3106	$892.32	$892.30	$892.30