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	$36.78	11.214%	$40.9045	$40.90	$40.90	$40.90
Purchase #2	$58.35	3.853%	$60.5982	$60.60	$60.60	$60.60
Purchase #3	$218.69	11.446%	$243.7213	$243.72	$243.70	$243.70
Purchase #4	$115.90	10.308%	$127.847	$127.85	$127.85	$127.80
Purchase #5	$109.31	12.570%	$123.0503	$123.05	$123.05	$123.10
Purchase #6	$213.79	12.538%	$240.595	$240.60	$240.60	$240.60
Purchase #7	$115.76	11.484%	$129.0539	$129.05	$129.05	$129.10
7 purchase totals =	$868.58		$965.7702	$965.77	$965.75	$965.80