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	$25.88	11.722%	$28.9137	$28.91	$28.90	$28.90
Purchase #2	$249.94	12.186%	$280.3977	$280.40	$280.40	$280.40
Purchase #3	$148.84	8.713%	$161.8084	$161.81	$161.80	$161.80
Purchase #4	$189.98	11.624%	$212.0633	$212.06	$212.05	$212.10
Purchase #5	$118.29	7.671%	$127.364	$127.36	$127.35	$127.40
Purchase #6	$178.71	8.599%	$194.0773	$194.08	$194.10	$194.10
Purchase #7	$182.25	7.684%	$196.2541	$196.25	$196.25	$196.30
7 purchase totals =	$1,093.89		$1,200.8785	$1,200.87	$1,200.85	$1,201.00