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	$148.85	13.373%	$168.7557	$168.76	$168.75	$168.80
Purchase #2	$36.94	3.655%	$38.2902	$38.29	$38.30	$38.30
Purchase #3	$49.37	11.497%	$55.0461	$55.05	$55.05	$55.00
Purchase #4	$192.70	13.389%	$218.5006	$218.50	$218.50	$218.50
Purchase #5	$174.87	4.300%	$182.3894	$182.39	$182.40	$182.40
Purchase #6	$42.56	12.616%	$47.9294	$47.93	$47.95	$47.90
Purchase #7	$21.81	11.381%	$24.2922	$24.29	$24.30	$24.30
7 purchase totals =	$667.10		$735.2036	$735.21	$735.25	$735.20