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	$12.54	8.424%	$13.5964	$13.60	$13.60	$13.60
Purchase #2	$166.83	11.223%	$185.5533	$185.55	$185.55	$185.60
Purchase #3	$21.54	8.544%	$23.3804	$23.38	$23.40	$23.40
Purchase #4	$50.82	4.763%	$53.2406	$53.24	$53.25	$53.20
Purchase #5	$233.54	9.856%	$256.5577	$256.56	$256.55	$256.60
Purchase #6	$100.60	10.143%	$110.8039	$110.80	$110.80	$110.80
Purchase #7	$198.88	7.383%	$213.5633	$213.56	$213.55	$213.60
7 purchase totals =	$784.75		$856.6956	$856.69	$856.70	$856.80