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	$6.86	8.339%	$7.4321	$7.43	$7.45	$7.40
Purchase #2	$239.40	13.141%	$270.8596	$270.86	$270.85	$270.90
Purchase #3	$115.73	6.764%	$123.558	$123.56	$123.55	$123.60
Purchase #4	$117.52	4.610%	$122.9377	$122.94	$122.95	$122.90
Purchase #5	$30.60	3.367%	$31.6303	$31.63	$31.65	$31.60
Purchase #6	$113.88	3.492%	$117.8567	$117.86	$117.85	$117.90
Purchase #7	$109.94	4.544%	$114.9357	$114.94	$114.95	$114.90
7 purchase totals =	$733.93		$789.2101	$789.22	$789.25	$789.20