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	$10.76	3.122%	$11.0959	$11.10	$11.10	$11.10
Purchase #2	$137.96	13.505%	$156.5915	$156.59	$156.60	$156.60
Purchase #3	$33.31	9.602%	$36.5084	$36.51	$36.50	$36.50
Purchase #4	$159.33	11.569%	$177.7629	$177.76	$177.75	$177.80
Purchase #5	$25.89	13.648%	$29.4235	$29.42	$29.40	$29.40
Purchase #6	$133.51	13.181%	$151.108	$151.11	$151.10	$151.10
Purchase #7	$75.91	12.775%	$85.6075	$85.61	$85.60	$85.60
7 purchase totals =	$576.67		$648.0977	$648.10	$648.05	$648.10