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	$73.31	13.744%	$83.3857	$83.39	$83.40	$83.40
Purchase #2	$156.95	11.537%	$175.0573	$175.06	$175.05	$175.10
Purchase #3	$43.34	11.784%	$48.4472	$48.45	$48.45	$48.40
Purchase #4	$78.62	13.391%	$89.148	$89.15	$89.15	$89.10
Purchase #5	$54.36	9.299%	$59.4149	$59.41	$59.40	$59.40
Purchase #6	$23.26	7.172%	$24.9282	$24.93	$24.95	$24.90
Purchase #7	$135.64	9.127%	$148.0199	$148.02	$148.00	$148.00
7 purchase totals =	$565.48		$628.4012	$628.41	$628.40	$628.30