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	$69.37	4.507%	$72.4965	$72.50	$72.50	$72.50
Purchase #2	$141.82	10.136%	$156.1949	$156.19	$156.20	$156.20
Purchase #3	$150.77	6.258%	$160.2052	$160.21	$160.20	$160.20
Purchase #4	$139.60	7.855%	$150.5656	$150.57	$150.55	$150.60
Purchase #5	$168.44	9.385%	$184.2481	$184.25	$184.25	$184.20
Purchase #6	$128.95	12.112%	$144.5684	$144.57	$144.55	$144.60
Purchase #7	$61.94	10.595%	$68.5025	$68.50	$68.50	$68.50
7 purchase totals =	$860.89		$936.7812	$936.79	$936.75	$936.80