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	$141.43	9.865%	$155.3821	$155.38	$155.40	$155.40
Purchase #2	$227.84	7.457%	$244.83	$244.83	$244.85	$244.80
Purchase #3	$106.83	11.398%	$119.0065	$119.01	$119.00	$119.00
Purchase #4	$105.64	11.346%	$117.6259	$117.63	$117.65	$117.60
Purchase #5	$118.36	9.114%	$129.1473	$129.15	$129.15	$129.10
Purchase #6	$203.50	3.720%	$211.0702	$211.07	$211.05	$211.10
Purchase #7	$114.75	7.389%	$123.2289	$123.23	$123.25	$123.20
7 purchase totals =	$1,018.35		$1,100.2909	$1,100.30	$1,100.35	$1,100.20