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	$137.57	5.753%	$145.4844	$145.48	$145.50	$145.50
Purchase #2	$48.43	11.111%	$53.8111	$53.81	$53.80	$53.80
Purchase #3	$227.93	5.319%	$240.0536	$240.05	$240.05	$240.10
Purchase #4	$99.39	13.264%	$112.5731	$112.57	$112.55	$112.60
Purchase #5	$75.62	9.579%	$82.8636	$82.86	$82.85	$82.90
Purchase #6	$54.77	7.596%	$58.9303	$58.93	$58.95	$58.90
Purchase #7	$231.60	9.524%	$253.6576	$253.66	$253.65	$253.70
7 purchase totals =	$875.31		$947.3737	$947.36	$947.35	$947.50