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	$243.73	4.452%	$254.5809	$254.58	$254.60	$254.60
Purchase #2	$43.27	11.683%	$48.3252	$48.33	$48.35	$48.30
Purchase #3	$240.30	12.371%	$270.0275	$270.03	$270.05	$270.00
Purchase #4	$52.63	13.647%	$59.8124	$59.81	$59.80	$59.80
Purchase #5	$112.68	3.335%	$116.4379	$116.44	$116.45	$116.40
Purchase #6	$65.26	9.507%	$71.4643	$71.46	$71.45	$71.50
Purchase #7	$243.75	11.709%	$272.2907	$272.29	$272.30	$272.30
7 purchase totals =	$1,001.62		$1,092.9389	$1,092.94	$1,093.00	$1,092.90