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	$243.54	8.509%	$264.2628	$264.26	$264.25	$264.30
Purchase #2	$131.67	3.831%	$136.7143	$136.71	$136.70	$136.70
Purchase #3	$82.84	9.650%	$90.8341	$90.83	$90.85	$90.80
Purchase #4	$18.76	4.535%	$19.6108	$19.61	$19.60	$19.60
Purchase #5	$58.28	9.723%	$63.9466	$63.95	$63.95	$63.90
Purchase #6	$5.33	8.232%	$5.7688	$5.77	$5.75	$5.80
Purchase #7	$73.45	7.392%	$78.8794	$78.88	$78.90	$78.90
7 purchase totals =	$613.87		$660.0168	$660.01	$660.00	$660.00