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	$245.25	11.327%	$273.0295	$273.03	$273.05	$273.00
Purchase #2	$74.81	5.399%	$78.849	$78.85	$78.85	$78.80
Purchase #3	$49.52	7.661%	$53.3137	$53.31	$53.30	$53.30
Purchase #4	$88.35	6.189%	$93.818	$93.82	$93.80	$93.80
Purchase #5	$11.90	7.779%	$12.8257	$12.83	$12.85	$12.80
Purchase #6	$227.40	11.638%	$253.8648	$253.86	$253.85	$253.90
Purchase #7	$178.50	9.836%	$196.0573	$196.06	$196.05	$196.10
7 purchase totals =	$875.73		$961.7580	$961.76	$961.75	$961.70