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	$43.45	8.162%	$46.9964	$47.00	$47.00	$47.00
Purchase #2	$173.54	10.410%	$191.6055	$191.61	$191.60	$191.60
Purchase #3	$45.92	13.489%	$52.1141	$52.11	$52.10	$52.10
Purchase #4	$174.60	12.365%	$196.1893	$196.19	$196.20	$196.20
Purchase #5	$40.38	5.545%	$42.6191	$42.62	$42.60	$42.60
Purchase #6	$92.61	11.790%	$103.5287	$103.53	$103.55	$103.50
Purchase #7	$196.81	13.771%	$223.9127	$223.91	$223.90	$223.90
7 purchase totals =	$767.31		$856.9658	$856.97	$856.95	$856.90