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	$145.81	12.871%	$164.5772	$164.58	$164.60	$164.60
Purchase #2	$147.75	11.360%	$164.5344	$164.53	$164.55	$164.50
Purchase #3	$208.90	13.635%	$237.3835	$237.38	$237.40	$237.40
Purchase #4	$16.90	9.453%	$18.4976	$18.50	$18.50	$18.50
Purchase #5	$135.30	12.285%	$151.9216	$151.92	$151.90	$151.90
Purchase #6	$98.30	4.374%	$102.5996	$102.60	$102.60	$102.60
Purchase #7	$237.60	11.833%	$265.7152	$265.72	$265.70	$265.70
7 purchase totals =	$990.56		$1,105.2291	$1,105.23	$1,105.25	$1,105.20